Rule no 1: Have two tubes and repair at home if you can, rather than next to the roadside.
Rule no 2: Remove puncture causing object from tyre before fitting new/repaired tube.
Rule no 3: Don't bother attempting to repair a puncture at the valve's neck or right next to the valve itself. It is futile.
Rule no 4: Abrade the patch area on the tube with sandpaper, not that funny raspy thing that comes with puncture kits.
Rule no 5: Never touch either the inside of the patch or the patch area on the tube with your fingers. Never.
Rule no 6: Apply rubber cement to tube only and let dry - 5 minutes at least. If it is raining and the tube is getting wet, start walking. It won't work.
Rule no 7: Don't remove the cellphane backing from the patch, only the foil.
Rule no 8: Apply patch firmly and exactly, It cannot be repositioned. Apply pressure,
Rule no 9: Don't attempt to pull cellophane off. Rather fold the patch/patched area over and score the centre of the patch with a sharp object so that the stretched cellphane bursts. Leave it on. You can remove it later. Attempting to take it off now may lift the patch.
Rule no 10: Periodically check if the glue in your saddle bag is still good. Replace once a year.
I keep a stock of tubes and patch in batches when TV is rubbish that evening. It saves on glue which inevitably goes hard in between patching sessions.
I never pay for tubes, they are discarded at large races and charities alongside the road. I collect them and fix them up.
Never suck on strange tubes to evacuate them for storage, some people inflate with CO2 and sucking on that isn't nice.