Well, the answer here depends on what you're looking for. Since the question was a bit vague, I'll try to cover the bases.
If you're looking for stat based answers regarding D&D, head over
here, specifically the races, Player's Handbook, and Draconomicon boards. They can help you out a lot in terms of advice on character building.
If you're looking for direction on a description for the ISRP, it's a matter of personal taste. Some half dragons are more human like in appearance, others more draconic, depends on the route you want to take. There's an excellent guide linked
here in this thread that will help with description writing in general.
If you're looking for roleplaying advice, again, this is a matter of personal taste, and is certainly the most difficult one to advise another person on. It varies by the type of half dragon, alignment, etc., there are several ways to go with it.
Hope that helps.
