pulling apart lenses is one of the best parts of my job, a bit like solving puzzles, especially when you don't have drawings or disassembly instructions. There's great satisfaction when you finally work out the trick that unlocks the next layer. Sometimes you need to start from the front, sometimes the back, sometimes both! Sometimes a lock ring doesn't have notches for a lens wrench to slot into, and you need to use circular rubber grips. I've made about 20 of those, of different sizes, using O-ring rubber cut and glued to the end of tubes. But certainly the main tools are jeweller's screwdrivers (or occasionally mini allen keys) and a lens wrench. You can buy lens wrenches on ebay for next to nothing these days. If the lens is junk I guess scissors would work too, but be careful not to cut yourself, sometimes undoing a lock ring can take a bit of force. To safely remove glass elements you need suction cups, but that's probably beyond what you're interested in. Some other tools I personally find very useful are tweezers, magnifying loupes, toothbrushes, cotton buds and most importantly a compartment tray to keep all the bits in. You can store the bits in sequence to make it easier to reassemble later.
A drop of acetone on tiny screw heads will soften any locking varnish, as Stuart mentioned. Lock rings and other threaded connections may also be varnished in, again a drop of acetone run into the join will help loosen things. Just be careful of some plastics or painted surfaces when using acetone. Some stills lenses have screws hidden under a decal glued on over the front ring.
Be careful not to damage the heads of tiny screws, once the slot or cross or hex is rounded off the only recourse is to drill the screw out. If a screw won't turn it's best to try some more acetone or even a bit of heat from a hair dryer rather than force it. Though I suppose it doesn't really matter if you're just playing with junk lenses.
Here's a photo I took recently of a Kowa anamorphic lens I spent some time overhauling, it has very clever dual focus mechanics where the focus ring moves both a middle anamorphic element via a cam and the rear prime via a helical thread at the same time:
Edited by Dom Jaeger, 24 June 2014 - 09:35 PM.