answer what you know and skip the ones you don't know, if you have a good answer then you have a chance at best answer. yes some users pick favorites and even mods sometimes but don't let that discourage you from answering if it's something you know about.
If you're answering questions just to get best answers, I think you're doing it for the wrong reasons.
I wouldn't worry about rose ratios if I were you. Many people don't give best answers. A lot of girls ask questions for conformation of what they want to believe rather than taking real advice. Many times multiple people answer questions the same way so someone might get picked over you. Furthermore, there are a lot of bogus and joke questions that if you answer will drop that rating. It's not hard to maintain about 5% but anything above that for any period of time is wishful thinking. My best answer rating was 100% for a little while. =P
I'm mostly guessing because I usually answer whatever, but I'll go about this logically. You should probably try to stick to questions that aren't anonymous. That way you can go on to the person's profile and check their previous questions to see if they regularly give best answers...or they rarely do. If they usually give a best answer your chances have just increased significantly. I would try to avoid questions that have a ton of responses because that makes it less likely that you'll get best answer. The only other advice I can give you is only answer the anonymous questions if nobody has really answered them and then you can hint at them to give you best answer. P.S. don't answer mind because I'm very bad about giving best answer. Lol.