The trick is (not that it's a trick) to think of the halt as a forward movement rather than stopping. The minute you think of halting as pulling on the reins and blocking forward movement, that's the second that your horse halts crooked and heavy on the forehand. Halting, in my opinion, involves walking the horse up into the bridle by stretching tall, stilling my seat and closing my legs ever so lightly to get my horse to step up into the bridle with his hind legs. With the reins, all I do is concentrate on keeping my elbows soft to make his head has somewhere to go instead of hitting a wall. If you do it right, you pretty much don't need reins. It's all in the seat. Hope that makes sense.