Gun, clan leader signs up for a landing battle, normally 8 apply, and are paired up, winner continues up the ladder till they meet the clan holding the territory. If you win the territory is yours till the next day when it all happens again.
As noted above, you'll need minimum of 20 active tankers that can show up every day, with 12 tier 10 tanks, and up to 3 tier 8 arty. Favored tanks seem to be T-110's, E-100's, IS-7's and to lesser effect Maus (good for blocking bridges, choke point) Batchats. TD's will get some action on defensive battles. I've been in several battles with my ISU-152 with mixed results.
Less than that and your odds of winning a landing battle are pretty slim.