Dd and ds both potty trained at 20 months. Dd was a more intense process than ds b/c we part time ECed with ds whereas the potty was pretty much brand new for dd when we started, but both accomplished it after a week of what I like to call "potty boot camp." Here is my general method (I apologize if the pronouns are wrong as I typed this out for a friend):
Summary (much more detail below...)
1. Naked time only, follow around vigilantly with the potty so that she knows EVERY pee and poop go in the potty
2. Once you have near 100% success, stop following her around and start to rely on her cuing you to use the potty. Still naked time so that she can sit on the potty by herself if she wants to and doesn't have to get her clothes off first. Depending on how naked time goes, you might be able to skip this step.
3. Panties (maybe pants, too). You may have to follow around again if she has trouble waiting for the potty and taking her clothes off. Again, depending on how steps 1 and 2 go, you might be able to skip this step as well.
4. Short trips out of the house, bring the potty and offer frequently. Play dates in home where you offer the potty frequently.
5. Transition to toilets instead of potties while at home as much as possible. Take her to the bathroom frequently when out and about.
6. Use toilets only with a potty seat and step stool (when she's able to mount the toilet herself). Wait for her to cue you when out and about.
7. Nap and nighttime dryness
Detail of my experiences
I do not believe in a reward system. I also don't believe in over praising. When the child is so young, stickers, candy, and charts aren't going to mean anything anyway. This is one of the huge advantages of early potty learning. A young toddler hasn't reached the stage of "I won't do it because you asked me to!" and therefore simply does things for the sake of doing them. You may have potty regression later on when she does go through that phase (usually around 3 or so), but I've heard it is short lived because they are so used to using the potty and really don't want to have wet pants. My dd did not regress.
We did not use training pants. In fact, dd found them confusing. They weren't panties and they weren't diapers, but she thought they more resembled diapers, so felt free to pee in them. We had two pairs (Potty Patty panties) and rarely used them. Instead, we purchased the 2T panties from Target and shrunk them with hot water and a hot dry. They are a combo pack of solid colors and animals, so no Dora the Explorer! LOL. But during the actual process of learning, she was bottomless and that's what did with ds as well. It wasn't until much later that we actually used the panties when going out and about. Instead, as you'll read below, we went for sort of a "hybrid" method. Other supplies you'll need are a good spot cleaning solution (I really like Bac Out by BioKleen) and lots and lots of rags/towels. Oh, and of course, potties! We used the Baby Bjorn (with the back support) and the little, more portable Ikea potty (so cheap!). Later, we also got potty seats for the toilets and step stools. Some kids prefer the "safety" of a small potty and other kids really enjoy using the big potty. After the initial training stage, it's nice to give them options when encouraging the potty: "would you like to go in the pink potty, the white potty or the potty seat?" This allows them a sense of control even though they need to use a potty one way or another! You can also replace your toilet seat with a "family potty seat" that has a flip up toddler sized seat inserted into the larger adult seat. These are really nice once she's going on her own.
Several other mamas in my parenting group had done early potty learning (though really when you do it early, I think it is training, not so much learning). One had accomplished it at 17 months another at 19. They both used a method that didn't really work for my dd's personality. We all did "boot camp" style where you pretty much stay in the house for several days to 2 weeks. But, they went the route of putting their child on the potty every half an hour for the first several days (set a timer to remind yourself). To keep them on the potty, they would sing songs, read books, play games, etc. Eventually the child goes in the potty and then a big deal is made of the event with lots of "you peed in the potty!!" and smiles and clapping, that sort of thing. Then you take the pee to the toilet and let them flush (always fun). Slowly, you lengthen the time between potty sessions as you learn their cues better. You will likely find that as you start this process you begin to see little, subtle signs that you had been missing before (this is the essence of EC, too). When you're used to relying on a diaper, you don't need to look for those cues, but when all your attention is on this one task, you'll see some signs. I also used this time to reinforce the sign for potty as well (shake the letter T).
This worked for them. However, when we tried, it was an utter failure. Dd wanted nothing to do with sitting still on the potty long enough to pee or poop. Her temperament is much too active for this. We also had the issue of very, very frequent peeing and pooping. She drinks probably 2 or 3 times the amount of water that her friends do and we (and my ped at the time) believe that her vegetarian diet makes her poop a lot, too. While it's good practice to have frequent excretion, it's also many more chances for accidents and required me to be much more vigilant than the other moms. To over come these challenges, I went the route of simply following her around with the potty. I let her go about her normal activities (in the house and a few walks in the neighborhood) and as soon as she started to pee or poop, I would shove the potty under her. For the first few days, dh and I switched off "being on duty" every half an hour or so or else we would have gone insane. By the time the weekend was over, we had seen little progress, which was very discouraging. But I stuck with it for another two days without help from dh and slowly I started to see her waiting a little longer between pees. I also started to see her pee almost immediately when I put the potty under her (cash in on the first pee of the day and first pee after nap as great reinforcement). These changes really made all the difference. Once she finally made the connection between, "I put you on the potty, you pee or poop" we could go places again. Whenever we were staying in one place for a period of time (like at the park, in someone's house, in the car) I would put her in diapers. But she never peed in them. I would take her to every public potty I saw and frequently at the park or in houses. Generally, she was so distracted by what we were doing that my frequent trips to the potty were enough to keep her dry. Of course, we had accidents. But, I preferred to deal with those than with diapers. At home we were always bottomless or in panties and I had more issues. I did a LOT of cleaning up of pee and sometimes poop. But it just kept getting better and better. When she was still so young, I would have the occasional regression day and with her high level of distractability, I would remind her every hour or so (if I remembered) and make sure we went before we left the house and before we left an activity. Watching other kids use the potty is also a great way to help reinforce this process. When they are young, they like to mimic each other, so expose her to every potty trained little kid you can find! I actually had a few of her potty trained friends come over to my house while we were house-bound and demonstrate. This always seemed to help. If you have two potties, they can go side by side. Also, be sure she comes with you to the bathroom every time you go. Have her sit on her potty while you pee (if she'll sit still!). Make a big deal out of "mommy is peeing in the potty and ______ is peeing in the potty! We both are peeing!" Keep things as fun and light-hearted as you possibly can.
Now, all this being said, it was a LONG time before she was doing this by herself. She still preferred to have help with the process until she was about 2.75 years old and it was also around then that we starting having success with her washing her own hands afterward. This is a long process when you start early, but honestly, I have seen other parents have to help their 6 year olds wipe after they poop, so the longer they practice the better they get at it at a younger age. As she got more verbal, sometimes she would announce that she needed to potty, but mostly, I was still taking her at intervals until she was well over 2. Also, naptime/night time dryness doesn't usually come until later. She started being dry during her nap a few months after we started potty training, but would still have set backs when she got sick. She started being reliably dry at night a little before 2.5 years. But these things were no big deal. I would use the same diaper for nap and night time- using only one diaper per day. Once she started being dry at nap, I reused the diaper for two nights in a row. Less and less washing!
With ds, things went much quicker and easier. Since we ECed him part time, he already knew the potty was for poop and pee. With him, we just needed to get him to understand to use it every time... in otherwords, to tell us or to go by himself. So again, we are staying vigilant and following him around, but he almost always communicates his need to go and has gone by himself a few times already! EC really was very helpful. He's been in underwear now for about three weeks and while we are having regression days once a week or so, overall, he's pretty much got it. He's already dry at night most nights and is always dry after nap as long as I get him on the potty quickly enough. So that part may come much earlier for him than it did for dd. Again, I attribute that to EC.
I think it's just important to follow your child's cues. If it seems like she's really unhappy in her diapers, then it's time for a change! If it seems like the potty training process is really wearing on her, causing a rift between you even when you're keeping things really positive and fun, then she's not ready and will probably accept her diapers back at some point and you can try again later. Temperament is really important to keep in mind, too. If she is "stubborn" or as I like to say persistent, this type of personality requires more patience through any milestone. I also believe that it will likely lead to one of two outcomes- complete and total mastery of the concept or a longer period of accidents. Some persistent children learn a concept so fully that accidents and regression are rare. Some persistent children fluctuate in what they are persistent about and therefore go through phases where they are completely competent and phases where they just don't seem to care (oh, are those phases frustrating when you're used to a child that has mastered a concept!). So, be prepared!
Anyway, that's what we did! Good luck mama!