I'd say simply having a friend who is doing the same thing you are is the biggest help. They feel obligated to go work out because they don't want to disappoint you, and you feel obligated to go work out because you don't want to disappoint your friend. Its a mutual thing, and I found that it worked really well for me a couple of years ago, until they closed the gym off
But if it hadn't been for that, we'd still be there, every day, working out.