So how do I eyeball a wing to check for warps and to rough check the aileron positioning?

You can use both eyes or one. The idea is to line your eye(s) up "straight back" from the wing and centered to the wing. Centering is easy. When you see both sides of the fuselage equally, you're straight back on that plane. Centering up and down isn't so easy.

If the wing is a symmetrical one, then before you start, look at it's alignment in the fuselage and trace along the fuselage to the rear to see where it's pointing. Start with that "point". If you're aligned up and down when looking at the rear of a symmetrical wing, you're going to see equal amounts of it above and below the trailing edge. Make that judgement by comparing the wing at the roots.

A cambered wing isn't really hard to do if you realize that it doesn't matter too much. You're not measuring the thing. You're just eyeballing, but you do need to establish in your own mind "how much shows above and how much shows below" and stick with it. Once you've got the proportions in mind, the rest is fairly easy.

Keep your eye(s) and the airplane steady and look left and right. Keep looking back straight ahead to check that you've not moved the plane or your head, and you'll start to pick up what's straight and what's not.

It helps to have the sun or lights directly behind your head but if that isn't easy to do, then it works to have light directly down on the top of the airplane. Comparing a solid shadow to a bright image isn't so hard to do because the outlines are sharp. Try to get a contrasting background and whatever the light is doing won't matter much.

Now, simply look to see where the TE of the ailerons goes compared to the TE of the wing. Then look at the TE of the wing and ignore the ailerons alltogether. It helps to adjust whatever you see wrong with the ailerons and then look again.

It's always a surprise to me how few guys have ever done this eyeball check. Or don't really know how to do it.

A couple of things have shown up sort of as a trend over the last year. It's amazing how good and straight most ARF wings are built. After looking at lots of wings from way before ARFs showed up, I gotta admit that the ARF mfg's are doing this hobby a big favor, or at least a favor to a lot of the guys in this hobby. But the other thing I've noticed is that the ARF mfg's are doing a universally lousy job of cutting hinge's into the wing/ailerons. It would seem that they almost always have misalignment somewhere. You'd think they'd use a tool or jig. Actually, you'd think they'd do some quality assurance and then fix their proplem however they chose. But they need to get better at that one detail. This one step isn't close to the quality of the rest that they do.