For an AK, I like the bolt body, bolt lugs, bolt carrier rails, and the recoil spring somewhat wet, but not dripping, with a moderately thick oil (I use Mobil 1 5W30 or 10W30---it's an excellent lubricant and it's cheap---but you can use whatever you want) applied using an oil-wet cleaning patch or Q-tip, as appropriate. Other metal surfaces, interior and exterior, get a very light coat of a thin oil (Rem Oil, for me) to protect against corrosion. The gun will function with less lubricant, but having it well lubricated makes cleaning a cinch; after five or six range sessions, wipe all the parts clean with a paper towel or two and re-oil. The gas piston just gets a thin coat of Rem Oil for corrosion protection while it's sitting, because oil doesn't stick around in the gas tube.
It's not the only way to do it, but it's what I do. Just don't use so much oil that it is spattering when you shoot the gun or leaking out; using a patch to apply it, instead of dripping it on directly, helps you get the amount right.