I made a few for the first time last week. The first two I made failed because they leaked. Apparently,the trick is to make certain that the two plates are perfectly even at the bottom. You can scrape your fingernail over the bottom and check that you don't feel a bump as you scrape from one plate edge to the other. Also, *lightly* place the plates into the gel casting device - don't push them into the gummy/rubbery bottom, since that will actually cause leaks. You can test for leaks by putting some 100% EtOH between the plates. You can then dump out the EtOH by turning the casting system to the side and letting the EtOH run off into the sink/pipetting the remainder out.
As for the actual casting, I just followed a recipe and it seemed to work. After the first two gels failed, I made four more and ran them successfully. Add butanol on top of the resolving gel as its setting to make an even interface. Wash the wells out with ddH2O before loading.