When I was a kid, we used to catch them at Springbank Dam in London. Having tried numerous techniques to not only get them to bite, but to also get them in, we found that using a small float, with about one foot of line below, with a treble hook and minnow worked best.
We would wrap the minnow around the treble, sometimes 'more than one, so that the fish saw a ball of minnows. We'd either hook them in the "nose" or just inside the mouth... they are tough critters to hook.
That all said, we got pretty bored catching them as the fight is little to non-existent.
@Moosebunk has posted some incredible Gar fishing reports, perhaps he could shed some light on the topic.