There are several things members need to know of your tank to answer your stocking questions. I have seen many threads in this part of the forum that must waste days as thread starters try to get back to people that inquire about these parameters.
TANK SIZE - Very important. Some fish work fine with bettas but need a fairly large tank by Betta standards (e.g. zebra danios). Please provide the tank size when asking any question here. Please note that tanks under 1 gallon cannot support a betta for any length of time.
CURRENT INHABITANTS - Some fish are not suitable for a betta, either if they grow too large, look similar to a betta, or may be preyed on by bettas. Others are fin-nippers and will wreck the beautiful fins of bettas (e.g. Tiger barbs). No aggressive or semi-aggressive fish, as they will more than likely pick a fight with the elegant betta.
TEMPERAMENT WITH EACH OTHER - I have seen too many threads asking if male bettas can be kept together, or if female and males can be correctly kept. If you have any questions, please visit this thread:
Betta Compatibility With Each Other
PLANNED pH LEVEL AND OTHER STATS - I don't mean to actually test the pH, but do your homework. You'll find that you can't keep bettas with Malawi cichlids, among other fish for the same reason, and not finding out lots about your desired fish species makes about as much sense as putting bogwood in that same Malawi tank.