While CDs aren’t as popular these days, they’re still around. At some point, I’m sure you’ve had to deal with a scratched CD. Instead of throwing out the CD everytime this happens, try using a cloth to polish the surface of the CD first. If that doesn’t work, here are a few other suggestions:
Toothpaste
Toothpaste – believe it or not, regular toothpaste (not the gel kind) works well for scratches on a CD. All you have to do is put a small amount on a cotton swab and rub over the scratches until you’ve removed them. This is probably the cheapest method that you’re going to find.
Metal Polish
If you tried the toothpaste method and that didn’t completely work, another alternative is to get some metal polish (like Brasso) and use a cotton swab to polish the scratch, and then rub a small amount of Vaseline on the CD moving from the center to the rim.
Skip Dr.
This is one of the more expensive methods that you’re going to find, but if you’re needing to repair an expensive Xbox game, this is cheaper than buying it new again.
Skip Dr. claims to fix scratches that cause your disc to skip and freeze. The kit retails for over $50, but Amazon sells it for $25.99 and it includes resurfacing fluid, a drying cloth, and a felt buffing square.
General rule of thumb
A general rule of thumb that everybody should know by now is that you hold a disc by the outer edges, or stick your finger through the middle hole. Often times problems with your discs will come from fingerprints and rough handling.
When polishing your CD, use a lint-free cloth and wipe the CD from the center and move your way to the edge. Don’t wipe in circles!
If you have any additional suggestions, or you know of something that has worked well for you, please share…
Source: Hardware Secrets

I usually just wash discs(usually GameCube games), then try running them repeatedly until they work. I’ll look at this guide next time I have trouble with a disc
Hmmm…never heard of the toothpaste trick.
Just make sure the toothpaste doesn’t have any grit in it. I think Colgate Total is one to avoid. If you brush your teeth with it, then bite down after rinsing out your mouth, you will feel the grit.
I wash my cd’s with water if they dont work. The tooth paste trick is new to me. Gonna try that out if a cd not work again.