Best way to clean my old CD’s

Old CDs comne in basically 2 species: one is that they simply need to be cleaned with one of the methods already mentioned. And two, they're scratched to the point that they're not playable. 

There are several mildly abrasive polishing mechanisms on the market. Mine is about 20 years old and still works well but is no longer made. It's a small battery powered machine that slowly rotates the disc while  the abrasive wheel polishes it. 

I've had a couple discs where this machine could not remove deep scratches.

I once picked out a DVD from the library that was unbelievably filthy.  It had scratches, divots, a corn syrupy like goo and ground chocolate in it.  This is the polycarbonate disc that was the most challenging I ever in encountered.  I soaked in the kitchen sink with warm water and Dawn for about 5 minutes before wiping it with a cloth.  I then probably had to do 3 separate spray and wipe cycles with isopropyl but I got it to play in the cheap Sony Blu Ray that I was using at the time.

Perhaps a higher end player would have been less forgiving?  At any rate if that plays, anything will.

Just my two cents (that aren’t made anymore)

I think there are two questions here:  cleaning dusty or soiled discs that are other in good condition.  I agree that an isopropyl alcohol solution is good for this. 
The other issue could be some scratches on the non-label side of the disc that affect its playing (might skip or the player might reject playing it).  Years ago, someone on a forum suggested something they have used — plain white toothpaste with no granules in it.  Toothpaste has mild abrasives that might help relieve mild scratches (deep scratches aren’t remedied).  I have used this on old scratched CDs with success.

I have not used this, but another person spoke of a product that can fill in deeper scratches, maybe like an acrylic spray?, headlight spray?, and helped salvage an otherwise unplayable disc.  🤷‍♂️   I can’t say if that works, but if the CD is ruined, what do you have to lose?  

Well I use 70% alcohol its cheaper than 91%..i used little on a ball of cotton ,wipe it on and let it dry naturally or use a fiber drying cloth.The end.

I have found that scratches and divots in CDs disappear with applying isopropyl and strongly wiping with a microfiber cloth.  I suppose if someone really purposely tried to damage a CD with a knife or scissors that might not do it, but we are discussing every day use here