How to ensure subsurf doesn't make wrinkles/folds

Hey! I’m new to 3D modelling, and want to become competent (not good :P) at it for the purpose of making long-term placeholder models for games.

So, I’ve been practicing modelling, specifically making attempts at creating meshes that subsurf correctly. There’s of course the obvious rule of “don’t use triangles”, but it seems there are other ways to make “bad” meshes that create these oscillation fold things when you subsurf them.

For example, I have this here:

When I subsurf it, it horrifically dies like so:

How can I avoid this? It seems to happen to me repeatedly.

I forgot all the subdivision terminology again after learning it for the nth time, so sorry if my answer doesn’t make sense.

In this particular case here, you had these folds because of that inner edge loop (highlighted in pic) that emanates from a loop from which another edge loop also emanates. Someone else will probably explain it with the proper terminology.

The best I can do is direct you here:

Oh- yeah, that is the problem; I see where they’re connected. DURRR, that was stupid of me. Fixed, thanks! xD