How should I say yes when he asks me out?

Tell him it sounds great. Then ask him what he has in mind and when. If he doesn't have something well planned or he just wants to "hang out sometime," then give him your phone number and ask him to call you when he decides what the two of you will be doing. Smile and walk away. This will force him to make arrangements for a date. It will help make him think. The date should be 4-5 days ahead.