[ultraman zoffy]

The trick is to know all your options for "working out" edges and straightening them. Masking is usually just the first step... once you remove the mask, you have to also know the techniques for cleaning up your edges. I do this by either using a toothpick dipped in alcohol to scrape away excess paint, or by deletion (meaning, painting over rough edges or overpaint by going over it with your base color).
As you get better with all these techniques, you'll find that you won't even need to use tape to mask edges in a lot of cases. A steady hand and knowing how to "erase" rough edges is all you end up needing. Oh, and spend the money on some good detail brushes too. Hope that helps.