I would say that its a bad idea for you to discuss broad generalities with non-liberty people. You wont win the argument because there is no specific point to talk about. Try keeping things specific. If you're arguing with a conservative about the size of the military, don't pick a contentious area to debate around. They're going to be pretty adamant about Iraq, or Afghanistan. They wont however disagree with you over a troop withdrawal from Italy, Guam, or Iceland. The same goes with a liberal. They wont accept the idea that instances of central planning don't work, but specific ones will.
Also, don't rely on harsh language. That gets people to automatically disagree with you, whereas not being a jerk will get people to agree with you. Using ad hominem attacks makes you look like an aspie thats why you don't say sky wizard, nazi, commie, jackboot. Don't use stock arguments. Think more. Using the Nazis or KGB is a pretty good way to fill the role of a fill in the blank bad guy, but more specific examples could be used, like the stasi, Pol Pot, etc.
Realize when people are projecting. A lot of peoples arguments come from deep seated things they think about themselves. If you use that against them you win the argument. The premise behind this is to compare the generalities they make to what a more objective look would yield.
I could add more.