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