I run into a lot of people that think that photographing infants is easy. Now, I'll admit, for the first few months, this is more or less true, seeing as how they don't move much. You do still have to take into account feeding, changing, naps, etc. So planning is what it's all about when they're little. But when they become mobile up until they become bribe-able, it's no easy task. I do love the challenge though!
The most important advice I can give on the subject is just to let them do their own thing. If they get cranky, stop, if they get hungry, let them eat, plan the time to allow for their agenda because there is no forcing a baby to follow yours.
They don't need to be perfect in order to be beautiful. The little ones are perfect enough to shine through regardless if they are looking at the camera or not, sitting up or laying down, smiling or looking pensive, that's what makes the whole thing worth it. At least for me.