Usually, it's the bottom two, followed by the top two. But, as PP said, not always! I've known babies to get the top ones first, to get the bottom two and then the two teeth that are outside the front teeth, etc...
Mine has one tooth at 9 months, it is the center, on the bottom. My friends SIL's baby got her first tooth on the top, but not the center. (I forget the proper name for the tooth, its the fang ones sometimes called dog teeth)
My daughter got her bottom two central incisors first. Then she got the top lateral incisors, and then her first molars on top. Now the central incisors and canines are coming in on top. The poor kid is a walking teething machine
But, she's got nothing more comng in on the bottom yet. So, I don't really go by when "they" say the teeth will be coming and in what order. The teeth will pop out when they're ready.
I think my ds has those pearls things where his top molars will be - I think they're fat pockets or something? Normal, whatever they are. I did hear about a kid whose top canines came in first, she looked like a vampire! So on occasion there is variance.