What's the best way to lower a 66 bug

There are generally lowering kits available which compress the coil springs a bit. An old-school hotrodders trick, but NOT one that is recommended, is to heat the coil springs with a torch, which will cause the metal to weaken and sag. Again, NOT recommended. You may also install smaller tires, which would lower it a bit.

I'm not real sure where the "heat the springs" idea came form for a beetle. You can do that to the old square body GM trucks but as stated not recommended. You need to invest in drop spindles for the front and reset the torsion bars in the rear about to splines or clicks. You can go ultra crazy and do a narrowed beam in the front with the spindles or there is always air bag kits. These are availible from Airkweld. Pricey but availible