I use the patch kits from the hardware aisle of the grocery store unless it's for a bike with narrow tubes. They work great.

The most important things are to scrape all the mold release off the tube using the supplied scraper or some concrete, and to wait long enough for the glue to dry. I don't think it's possible to wait too long. Clean the tube, put the glue on the tube and patch, and leave it overnight just to see.