it is extremely important to have a main, but the legend which you are maining has to be good.
here are some best choices:
-Hattori
-Lucien
-Any gauntlet legend
-Any legend with new weapon, like currently scythe

Actually I'm joking. You only have to know how to jump, maybe dodge, and of course sigs. if a sig is strong, spam it. if you're hattori, you can use nsig all the time and you'll win. For gauntlets, you have to know a combo: slight into nair into sair. You can also start it with dlight. If you master it, you'll get to platinum in no time.

And about new weapons like scythe: Just use light attacks, nobody knows the moveset anyways so they don't know how to defend.

It is obvious that this game is pay to play. If you have a taunt, you win.
Just use it when: You kill your opponent, when you die, when you did an epic combo, and of course set it to your victory & defeat pose.

Here are some examples of best taunts to buy:
Deal with it, bow, wave, calculated, the reads, the running man, avatar flag, thumbs up, and the most important one:

SO SALTY