When leveling in CoV, there comes an inevitable time where you are competing for mobs with other Villains in the "common areas" of the game. In other words, in and around Fort Darwin and the city where you interact with other Villains.
Here's an easy way to get an unlimited supply of mobs available for you EXCLUSIVELY by using instances. Here's a quick example.
Around level 3-4, Kalinda gives you a mission to kill Sapphus, a local snake boss. Sapphus hangs out in a cave with about 15 of his minions just steps away from Fort Darwin. If you enter the cave, and kill EVERYTHING but Sapphus, you will take out around 15 level 4 mobs and get some excellent experience in a pretty short period of time, and all these mobs are exclusively for you.........zero competition with other Villains. Now, if you actually kill Sapphus.......the goal of the quest which opens the instance you can no longer enter the cave. So essentially what you do is wipe out everything in a specific instance, except the main "boss" of the instance. At that point, exit out of the instance and logout.
After you logout, log back in and reenter the instance. All the mobs have returned at this point, and can be run through again for solo, exclusive XP runs. Please note, if you DO NOT logout after leaving the instance and just reenter the mobs you killed previously will still not be there, it is essential you do the logout/log in deal. Some may say logging out/in is a 40 second process, and this is true. However, ask yourself how much time you waste running around a common area trying to find 15 mobs which aren't being attacked? That process can take you well over 10 minutes during crowded times.
This is an excellent strategy to use for leveling in general, use these instances to your advantage!