#1) Avoid talking about politics in the first place.
I mean, if you think George Bush is the Truman of his time, a man who will be vindicated by history for bringing freedom to the Middle East and your friend thinks he's Hitler, it's going to be hard to bridge the gap -- especially since there are probably 50 issues where you have that big of a disagreement. So, try to stay away from politics in general.
#2) Be big enough to handle disagreements.
If you can't handle the fact that your friend thinks Michael Moore is a cinematic genius and that Barack Obama is a "lightbringer," then how are you going to be able to hold up your end of the friendship? You have to just realize that you're not going to agree on some very important issues and deal with it.
#3) Correct them gently.
I hate to be this blunt, but in my experience, the average person thinks it's very important to know about politics, but simultaneously, is horribly uninformed about the subject compared to the typical person who reads blogs, listens to talk radio, etc. So as a general rule, most people believe all sorts of things that are ridiculous, completely incorrect, that some "friend of a friend" told them, etc.
With that in mind, if you are well informed, it's generally very easy to make them look like an idiot. Don't do this. Feel free to politely disagree with them if they are wrong and then move on. If THEY ask for a follow-up, explain your opinion, in neutral language -- and then try to move on from politics.
#4) Do you want to be friends or do you want to prove you're right?
I'm not saying you should go along to get along, because I don't believe in doing that, but people get very sensitive about how little they know about politics. If you rub it in their faces or make them look like idiots, which incidentally, is what generally makes for a good blog post =D, it's going to upset them. It's one thing to do that to liberal bloggers or liberals in a comment section, whom you probably don't care about one way or the other, but it's another thing to do that to your friends and family. So, let them know you disagree, but don't make a huge issue out of it or humiliate them.
#5) Remember that people are not groups.
As a group, liberals suck. They're dishonest, selfish, hedonistic, and slowly eating away at everything that's good, decent, and worthwhile about American society. However, your friend or a family member is not "liberals;" he's just a person. Treat him like an individual and don't try to make him bear the sins of liberals everywhere. That's too heavy of a burden for anyone to bear.
#6) Just realize it may not work.
I find that there are liberals and then there are fanatical liberals. Liberals who aren't all that into politics, you can have fairly normal discussions with. On the other hand, the fanatical liberals tend to infuse politics into every part of their life and if you are conservative, they genuinely see you as a bad person just because you don't agree with them. Realistically, you're probably not going to be able to be friends with someone like that, no matter how great you are as a friend, unless you want to be a doormat who spends all your time getting browbeaten and pretending you agree with him.
The Six Steps To Dealing With Liberal Friends And Family - Right Wing News (Conservative News and Views)