There are two ways to get to Legend Tier.
1.) you have to have at least 50 ranked rounds and your average has to be at 61 or lower and you will become a Legend. This is the best way to get to that goal.
2.) You can beat Legends in match play, or win in Ready Go's consistently and that will reduce your average (no one knows the formula for that) and you will become Legend. There are lots of Legends that have reached that tier by going this route, but I wouldn't recommend it. The reason why I wouldn't is because without gaining the true playing experience that you will gain from actually scoring and achieving the goal, it will come back to haunt you when you do get to the tips. To each his own however.
After you get to Legend Tier, you will have to play 500 rounds before your average saturates and you stop going up in average when you have a bad round, and you will have them. It can be incredibly frustrating playing and watching your average go up and there is nothing you can do about it because you are not "saturated". But, once again, to each his own. Just having the Legend Tier beside your name looks good but it won't feel good unless you can truly compete at that level.
This is a great game and it is one that is built on good stiff competition and a lot of fun. My advice to you would be to shoot the scores, keep learning, and be fully prepared for Legend Tier when you do achieve it. Whichever way you chose to go, I wish you luck and lots of fun with the game.