It's one thing to know how to swap between Agents in Agents of Mayhem, but it's another entirely to make sure your squad is super fighting fit. This means leveling up as much as possible to take on the enemy mobs out there waiting for you so they can take you out. Plus, there's the fact that every agent actually starts out at level 1, so you've got to make sure you get them all ready before throwing them out into battle depending on where you are in the game.
How to Gain Levels Quickly
Unlike some games where leveling up one character gives you equal footing across all of the others you have on your squad, Agents of Mayhem makes you level up each one differently. It's important to remember this, as though there are some upgrades you can grab via the Ark, but they don't apply to every single character every time. To that end, here's how you can make the most of leveling your characters.
Make sure to remember the many, many missions available to you in Agents of Mayhem as well as the side quests sprinkled throughout the game. You can always visit the Missions screen and check out the map for a list of what you can complete at any given time. You'll earn cash, experience, and other items for completing all of these missions, even if they happen to be out of the scope of your campaign. Take the time to finish them, despite how tedious it can be to continue completing some of the same objectives over and over. It can only bolster your time with the regular story missions.
Similarly, you can also seek out Contract missions, accessible via the Missions menu. These pay out quite well if you're looking for rewards in experience, and you can finish them out on your own time. If you have friends you're playing with who are also looking to earn additional levels, you might take them on to challenge them for other Contracts that need completing out, and receive experience in droves for having done so.
Unfortunately, there is no magic panacea for leveling up quickly or any sort of Rare Candy like we see in Pokémon to get you additional levels. You'll have to keep working hard if you want to rise through the ranks, so keep that in mind when playing. Be diligent, and don't ignore the rest of your Agents to favor just one. You should be fine then.