Not trying to be rude but I would think it would be detrimental to a horses training if you didn't even know what a lead is, before i even started cantering my instructor taught me leads, before i started trotting i was taught to post/diagnals and before jumping i was taught jump position over poles. not saying your not doing a good job because i don't know it just kind of seems backwards to be learning the correct way of doing things after you've already been riding. And i totally understand if you can't find and instructor so Books and videos would probably help a lot.. Probably videos more so.
Heres a video i found of leads that might help :) Getting the Correct Canter Lead - Bing Videos