generally, give them soft, quiet, acid water, plenty of live food and exercise... get at least six for a good chance to get a mated pair...put on some Barry White when you think the moment is right, and hope they do the nasty.
Angels are cichlids, keeping them from breeding would be problem, getting them to breed is not. For a pair you should have at least a 40 gallon tank or so.
Chucky and Jim are right. In my experience you should try to obtain a locally bred pair; they are more likely to be used to your water and are usually cheaper. They like to breed on slate, but mine were always breeding on the filter uptake tube.
They take good care of their eggs! They fan them and move them around. It is fun to watch them lay the eggs too.
