It was easier for us to get on a routine of morning and night unless she had eaten something really gooey then we would do an extra brush afterwards. We also flossed pretty early because my daughter has teeth that are crowded. We used the little flossers that have handles (I think Walmart has ones with dinosaurs, princesses, etc) and did this every-other night.
Make sure she's drinking water with flouride as well and getting regular checkups!
:)
Hope this helps!
Amanda
PS- My dentist recommended using a "spin brush" for her, but I can't remember what age we started using it. It gets rid of more plaque. Might want to ask about that too.