Ten Ways to Help Your Players Hate a Villain
1. Give him a magic item or gadget that one of the players wants. Have him use it on the characters with great enthusiasm.
2. Have him take credit for cool things the characters have done. If possible, have him collect a reward for their effort.
3. Give him an ally who is a genuinely good and nice guy and who is also friendly and supportive of the characters. Have this ally try to get both sides to get along, and sacrifice himself to keep his friends from fighting. Then make sure the players see the villain's absolute disdain for this ally.
4. The villain should only rarely defeat or thwart the heroes. Instead, he should make things much more costly enough for them, costly enough to taint their victory. Give him an objective that is tangential to the goals of the PCs, rather than in direct opposition, so he can take advantage of their efforts. Make sure he thanks them.
5. Have NPCs who do not respect the characters respect the villain.
6. Have the PCs find the one chink in his villainous armor—the one good thing he does that he keeps secret. It should be something hidden but clearly good, like charitable giving or teaching kids to read or something. Make sure that the characters get at least one crack at him while he's doing this, so they would be forced to act in front of the people who think he's a hero.
7. If the villain is going to kill someone, it should be someone who is about to help the characters. Ideally, he should also frame them for the murder.
8. Have him do exactly what the characters would do in that situation. If that thing has gotten the characters in trouble or made them look foolish, make sure that he is acclaimed for it.
9. At some point the villain should know something the players need to find out. He should be utterly civil and willing to help them out, but the price should involve them doing something for him that is difficult (but not impossible) and plays very much to their strengths, so it is very clear that whatever it is he could not have accomplished it without their help. Make sure the fruits of those labors show up again later.
10. Have the villain think highly of one of the characters, albeit in a very condescending fashion. Have the villain offer words of encouragement and suggestions for how to improve whenever possible, and make it clear he thinks the character has so much potential and it's just a shame he's not living up to it.