Something I have noticed, is that matching the tube size to the tire helps reduce the number of failed patches. When the tube has to stretch to fill the inside of the tire, it puts more stress on the patch and they start to pull away. I use the skinny tubes in my 25 mm tires and wider ones in the 28 and 32 mm tires.
I always use a kitchen timer to make sure the glue in thoroughly dry. I have also made patches out of old tubes, as well as rejoining the ends of a rubber rim strip. When gluing two pieces of rubber (vs. a patch), I put glue on both surfaces and let it dry before joining them together.
Those old Camel heat vulcanizing patches were the best, although I don't think they made any small enough for bike tires. My parents owned a truck stop in the 1970s and I put a lot of them on truck inner tubes. The second-hand smoke from one patch was probably equivalent to a pack of cigarettes.
