Actually, it also depends on the verbs you use. Some verbs go with "to sb." and some verbs go with "for sb.".

Think of “to you” as “in your direction”. And think of “for you” as “on your behalf” or “instead of you”. This probably doesn’t cover all situations but it might be a good guideline. If I say something “to you” it means my words are directed at you. You are the audience. If I say something for you, maybe you were supposed to say something but I said it instead of you.