Back to basics
 

Maybe it's my moniker, but I get a lot of flats. Probably not my moniker actually, flats are probably common for cyclists that hit the streets with 700-23 tires inflated to 125lbs. My problem is patches that don't hold. Probably less than 50% of my patches hold, and any hints to improve my average would be appreciated.
Some things I've garnered with experience:

• Self-adhesive patches are not as reliable as the old fashioned glue-on type.
• The glue instructions say to put a thin layer. Slap on a thick layer of glue.
• Pay attention to the instruction to wait 5 minutes for the glue to dry. Impatience will be counterproductive.
• Always take a spare tube along as well as a patch kit.

Buy your patch kits at the automotive section of a department store, and NOT the bicycle section. You'll get about 3 times as many patches for half the price.

large enough
 

Make sure the area you glued is really larger than the patch. When one is curved it can be hard to tell, so overshoot.

other than that, I have nothing else to add, you've done a good job.

How are you getting the flats? Have you tried a kevlar lined tire (Conti Gatorskins or Specialized Armadillos or ??? )

If it's at all possible to do so, change the tube in instead of patching on the spot. When you get home you can patch up the old tube, inflate it very slightly and leave it standing somewhere for a few days, and once you know it's not leaking anymore (cause it's still standing up and not sagging about) you can deflate it and carry it around as your new spare. That way the patch gets time to cure properly, instead of having to hold 125psi within a few minutes of being put on.

Even better, throw the punctured tube in a box. Then, on some rainy Saturday, you can get out your patching stuff and do a whole batch at once.

I don't agree with a thick layer of glue. I smear it thin, but ensure the layer is complete and little larger than the patch. A thin layer dries out quickly so the waiting part is minimal. Make sure to clean the area well before applying the glue. My failure rate is pretty close to zero.

Automotive patches tend to be fairly thick. Usable but thick. A lifetime supply
of patches is available in boxes of 100 made in Germany is sold by such as
AEBike for $15-18/100 depending on size. These are round 15 or 20mm in diameter.
8oz cans of suitable cement are in the Wmart auto dept and last 5yrs or so til they
get too thick to use. I keep the little sealed tubes of glue in the bike packs for
remote use on the road. I find it helpful to keep an old rim around with rim strip and
mount the repaired tubes on the rim for a few days to make sure they hold air.
This also tends to prestretch new tires making them easier to mount later.