Run your fingers round the inside of the tyre first
Find the cause first
Mark where the hole is on the tube, line the tube up with the tyre, and feel carefully around that section from the inside.
Patch properly
Roughen, glue, wait three full minutes for the glue to go touch-dry, then patch. The waiting is the part people skip and it is the part that matters.
Refit without pinching
Inflate the tube just enough to hold its shape before fitting. Most second punctures are pinches from the tyre levers.
