I'm not quite sure, but from what I gathered it is based almost entirely around money earned and troops sent (and partially towers placed). Money earned includes money from the goldmine and money from mobs killed. Mobs killed make a large amount of money and thus have the most weight out of anything else (which is why smaller teams or those which only defend and do not attack will almost always have their players in the top 3). I ended up in a 1v1 a couple days ago and despite winning the game got #2 on the other person got #1. So if you are aiming for #1, focus on placing towers to kill mobs and/or upgrading your goldmine. As I mentioned earlier, the towers you place also factor in slightly. I noticed this because I started a game and the entire other team left a few seconds in, but my teammate had placed a tower and got #1. I hovered over his name in chat and it showed he had earned more points, which had to be from the tower he placed since it was too early to send mobs. So if you're about to win a game, spamming a few towers down will help you earn a few more points. The ranking system in this game is pretty ridiculous, so I rarely try to get on the leaderboard. If you wanna win games (especially when you rush) you will likely have to abandon the #1 spot on the leaderboard. But anyway, I hope this has helped. :D