I think the biggest mistake some patients make when it comes to lip fillers is adding too much product too quickly. Their lips are not in balance with the rest of their face, and they simply look "done". The goal should really be a natural, elegant result, so I recommend using a product like Juvederm, and starting very conservatively (perhaps 1 syringe total, divided between the upper and lower lips) and then wait a week or so to see if you are happy with the fullness. If not, you can always add more, but this gives yo more control over the final result.
Just like with any cosmetic procedure, the goal is to look your best, not to look like someone else. If you keep this in mind, pick the right surgeon for your procedure, and perform the procedure cautiously, you will get a very nice, full, but natural result.