If you use masking tape make sure you press the edges down firmly so paint doesn't run under, make EXTRA SURE your paint layer (the one you're putting the tape on) is completely dry before doing this otherwise it'll pull it off.
Go to a model store,or a train&hobby store and get good model masking tape. "pactra" is a brand that I use and have great razor crisp lines while using it. Again just make sure you press hard down on the edge and you will be fine...oh and don't pool up paint..go in light coats or any mask will bleed.
yes, listen wisely to the above posts. That was my first learning curve mistake. If you don't press on those edges, you will get leak through, definitely.
Since you guys are all here, what do you all think about removing the tape before the paint is completely dried ? I feel like I get a crisper edge if I remove the tape just before the paint gets tacky (although you do run the great risk of pulling up the fresh paint as well!)
When I remove the tape I wait till its completely dry or damn close. I've had a couple instances where the paint wasn't totally dry and it would pull up parts that were leaving a very uneven finish. Now I wait until it is not tacky. Same is true with liquid mask.
If they do leak through and it happens, cover it up through weathering. Dry brush of your base silver over the leakage. As long as its not a big leak this can save you from having to start over.