Be sure to master that race you have chosen until you have become very good at plapying them. Just make sure the race you choose is a wise decision. When you pick your race you must understand that a ton of other gamers will have picked that race to work with as well. So you need to focus on improving your skills fast. You can become a pro but first you need to master the skills of the races in game. Make sure you understand the ins and outs of every unit so building good armies will be no problem. Understand what each race and unit is capable of so you sharpen your skills.
Also be sure to learn the basics of the other races. The time will come for you to attack your opponent so be sure to throw everything you got at them when the time comes. Get in the game with ease by understanding the basics of each class. If you want to be diamond then there is no other way around having to master the basics.
Get good with a guide like Shokz Guide to help you dominate.
It is key to build on any failures you may have went through. Build on the poor losses you went through by understanding what you did wrong. Hard work and study will get you far with this game.