If I ask you for advice, will you help me? - This basically asks what someone is currently willing to do for you. i.e. "If I do X in the future, will you do Y?"
If I asked you for advice, would you help me? - This refers to a past, hypothetical situation. i.e. "If X had happened, would you have been willing to do Y?"
Essentially, the first sentence is in the present tense and refers to a current situation, where you are asking the other person if he is willing to help you if you need him. The second sentence refers to a time in the past, and you are asking what the other person would have been willing to do for you at that time. The first sentence is correct, the second would be better as, "If I asked you for advice, would you have helped me?". Which sentence is better depends on which message you are trying to convey.