How to find better equipment
Marvel's Avengers is like a lot of games of its kind in terms of distributing new and better material to players. Just playing the game and picking up the items you find naturally is one way to get better gear. As you continue to level up and level up your character, you will see that the equipment you find will get better and better. There are a number of different activities in the game that will reward you with materials. These aren't limited to random loot boxes you can open, enemy drops, defeating bosses, or completing puzzles.
It's actually quite easy to find new gear in the Avengers game, as is often found by just playing the game as you naturally would. There really is no need to farm any material in Marvel's Avengers, as it can be found quite often as a reward.
Boost your gear to make it better
Once you have a piece of gear that you like, you can boost your gear to improve it. This can be done in the character option menus. Open this menu which will have several tabs at the top which include: Objectives, Skills, Equipment, Cosmetics, etc. To upgrade your gear, you'll want to go to the Gear section of this menu and then hover over the piece of gear you want to upgrade. Each item has different resource requirements. As you hover your mouse over the pieces of gear, a map will appear that shows the different aspects of the piece of gear, its power level, rarity level, perks, and more. This map will also let you know if a better power boost is available (at the top) and at the bottom you will find the resources to upgrade the equipment. Assuming you have the necessary items to boost, you can follow the prompt at the bottom of the map to boost. Hold the button down and it will consume resources, increase your gear, and improve it.
DNA keys will guarantee you better rare equipment
DNA Keys - Keys that can be farmed or earned that unlock DNA chests. A key unlocks a safe. Items in these chests guarantee at least one blue rarity. So how do you get these keys? You have to look for missions that have DNA key drops as a reward. As you move through the levels of the war table, simply look for the DNA keys as a mission reward.