There are tons of bonuses you can add to your player in order to increase your earnings:

Your League matters a lot - that's why I suggested focusing on going up the leagues early on.
The Arena you're playing in also matters, so going for the more difficult Arenas increases your bonuses But might reduce your chances of winning, so make sure you weight all the pros and cons here.
The Video Boost should be kept active at all times, as it gives you a huge bonus if you watch an ad.
The Collection bonus gives you points based on the number of items you have - this grows nicely over time
The Zlatan bonus is something you should focus on. Each day, you can collect during the tracks letters to form the word "Zlatan" and each gives you 10% bonus. That's why it's imperative to collect all the letters, as soon as you see them, even if that means you get a horrible time. Letters are most important!
Sponsorships unlock once you hit level 10, and they offer even better boosts to the bonuses.