My daughter is 3 months old, what can I do aside talking to her to develop her brain?

Other than talking to her, you can sing to her or do flashcards with her. There are infant flashcards by Glenn Doman. Do check it out. For me, I read to her a lot and let her play with interactive Lamaze cloth books and toys.

A lot of touches e.g. baby massage, flash cards, story books and etc.

thanks