The game has various Missions that you can take on to earn extra bonuses such as score Multipliers. To see your current mission, tap the menu on the top left corner of the main menu. You can also access this by pausing while playing - this is useful if you happen to forget what you are supposed to be aiming for mid-run.
You can tell when you have completed a particular mission because it will inform you after the run, telling you what exactly it was that you did to complete it. Some Missions are cumulative. This means that, using Coins as an example, they will add up the total number until you reach the goal. So if you are required to collect 1,000 Coins, you can visit the Missions tab to see how many you have done so far on your way to that goal. The game also uses Missions such as 'Spend 2,000 Coins' to get you to part with your hard-earned Coins.
As well as these Missions, you are also able to take part in various Daily Challenges. These change, as you might expect, once each day, and reward you with a special prize each time. Daily Challenges tend to take the form of collecting a particular string of letters to make up a word, such as 'B L A S T'. Once you get them all you will receive a bonus, usually more Coins.
This is an example of one of the letters in a Daily Challenge task