I suggest you to read some articles that were posted in this website. Use the search in the upper right corner. Also, I think I've seen this question posted in some other thread discussed before.
It will all depends on your necessity.
I am 3b (with a patch of 3c on top) and try to co-wash 2 times a week, unless I have to go to someplace and need my hair to be at his best, but I have this spritz bottle with water, conditioner and some olive oil and I refresh my hair every day, sometimes even twice.