click the ranking tab at the top of the in game screen, then on the left of the screen click continent tribes. that list is the tribes in your continent and the rank that they are for that continent. have a check through see which is the tribe for you and maybe they will invite you after you send a message askin for one
Just because a tribe has the most points, it isn't necessarily the best. Also look at ODA and average points per player before you join a tribe. Also, check their members for activity.
Take great care joining a tribe, it should last you the rest of the game.