Feel free to add to this thread, never too late to learn something!
2 for today;
when preparing to use a hole saw, dress the set off the outside of the saw, back to where its straight down the face. You will get a much neater hole, doesn't wander near so much and actually get the diameter you wanted. While you are at it, make sure the centre drill is straight and only protrudes as much as you need (ideally thickness of the material you are drilling through IF TUBE OR SHEET. Cut in bursts of only a second r so, cut slowly and use some lubricant (WD40 at a pinch)

If you are going to try to shape alloy panels it's unbelievably easier if you anneal it (unless you are using grade zero). To anneal, scribble over the area you are going to work with a Sharpie pen (permanent type). Fire up your MAP or similar type blowtorch and warm the panel until your scribble disappears. Allow it to cool, then start work. If it becomes difficult, that's called Work Hardening, so just repeat. It might not be the technically correct method, but it works.

If I might add...

When making a former or piece of bodywork out of layers of polystyrene, that needs to be sanded or surformed.
Do not glue them together, or at least don't allow the glue to spread to the areas that are to be sanded.
The glue line will sand at a different (slower)rate than the bare polystyrene, thereby creating ridges that are a real pain to deal with.

Computer and holes.

When I need to make holes on a specific radius, but I do not have a divider or specific device, I use a drawing on the PC.
After printing and collage on the metal, I just have to make my holes ....

Hi,
To add to Chris's drill advice...once you've drilled the pilot hole change the drill in the holes mandrel to a piece of round bar and use that . there is now no cutting edge to allow the saw to wander.
Ayrflyer

Yes, good idea, though I've never had a problem with wandering, possibly because I mostly use holesaws in a drill press.