What is the best way to glue two pieces of rubber together (regular glues don't work very well)?

Go to a hardware store and pick up a tube of rubber cement. Hope this helps.

depends on what you are trying to cement together.

If its roof membrane Rubber EPDM cement it chemically

bonds the rubber. If its just like 2 pieces of rubber try

rubber cement, or tire vulcanizing Cement. Tire cement

melts and forms an extremely tight bond.

The very best Glue for bonding two pieces of timber is a glue that goes by the trade name LUMBERJACK , I have used this glue for years in my trade ,Once bonded it really does hold.

Contact cement is probably the best. Elmer's make some and there ar others.

Make sure of the fit. Spread evenly on each piece and let dry. Align the pieces together and clamp for a few seconds. That should hold.

I don't know if its publicly available but theres a type of glue used in

the tire industry for retreading tires. Check at the autoparts store. A resin glue might work too. It depends on what rubber item you are gluing

Get a tire patch kit and use the cement in there, following the directions for applying the patch.

Have you tried rubber cement?