Develop some realistic expectations about how you will spend your days....and then throw them all out the window!!! When I became a SAHM, my daughter was just about to turn two. I had these fanciful notions about how much time I would now have, and all of the things I would get done. And then reality set in. You find that, in actuality, you have very little "free" time, and at the end of the day, you sit wondering just what it was you did all day.
I didn't have the time that you do to sit and think about it or plan, although I'm not sure how much of a difference it would have made. Some of it you just have to find your own way with. I do recommend things like storytime in any venue that may offer it. We attend one every week at our local library, but I know that both the Barnes and Noble, as well as the Chick Fil A in my area offer these (free) as well. That, more than anything else, was my salvation in making the transition to being a sahm. We went every week, and gradually got to know and make friends with some of the other "regulars". It was mostly beneficial to me in that it gave me a chance to meet and interact with other moms, and was a great source of not just friendships, but learning what other moms do to fill their days, and keep their little ones occupied. From their alone, I leaned about a mom's group, which meets bi-weekly for two hours, and had childcare. I found friends to have play dates with, as well as learning about all of the fun, cheap, or even free things to do with my toddler. I still live in the same area I grew up in, but had no idea about even half of the stuff that was out their for little kids.
Another great resource for me (lately) has been http://playathomemom3.blogspot.com. Their are so many great ideas for things to do with little ones that my non-crafty self would never have come up with on my own. Most of these are fairly inexpensive as well, and my daughter and I have absolutely loved them! I honestly think water beads are the neatest thing ever, and have yet to find a kid of any age who isn't instantly obsessed with them!