If your daughter is showing interest in the potty or what is going on in there, taking her own diaper off, or seems to be really noticing when she goes bathroom- like she needs to be changed right away and lets you know that- it is probably a good sign to start. We are thinking of getting a potty seat for ours right now, because there has been some interest- but we aren't going to push it.
I heard that after or around 2, if thye are ready, is a pretty good age to start introducing the concept- a lot of what other people said about allowing her to sit on the potty in non-stressful ways is good, and the other thing that is importatn is how long she can go with a dry diaper- like if she can go at least two hours- or if she sometimes can go through the night without it being wet- then she is likely to be ready to start potty training- but each child is ready at their own pace, so it is important that you don't let it become a big, stressful, scary thing. Everybody Poops is a good book, and there is one that has the flushing sound that I've seen a lot of kids enjoy, but I can't remember the title of it.