In the first scene, when you're getting the tour with the scrap robot, follow him all the way through to the small campsite with the car up on the lift next to the burning tires. Collect all the loot (guns, money) along the way and kill all of the guys. Once everyone is dead simply pause the game and go to exit. It will save your character (level & loot) and start you at the very beginning upon loading your game. You can repeat this as many times as you'd like!

To make a copy of any item you'll need a cooperative partner in a multiplayer game. Simply drop what you want to make a copy of on the floor, exit the game without saving, leaving your friend free to grab it. When you return, you'll have your copy of the weapon still, and your friend can hand you the other. This works on all guns, shields, and class mods, and can be done as many times as necessary.

In the first scene, when you're getting the tour with the scrap robot, follow him all the way through to the small campsite with the car up on the lift next to the burning tires. Collect all the loot (guns, money) along the way and kill all of the guys. Once everyone is dead simply pause the game and go to exit. It will save your character (level & loot) and start you at the very beginning upon loading your game. You can repeat this as many times as you'd like!

Watch your reload animation. As soon as the cartridge is removed (or rounds are being inserted), perform a melee and the gun will finish reloading. Do this to save time and possibly your life.

As soon as you are able to get a vehicle, find a safe place away from enemy spawn points and find a way to keep the trigger held down (tape? rubber band?). Just walk away for a few hours and after you have unloaded 100,000 shots from the vehicle you will get 20,000 exp.

After you've defeated Sledge (and collected the artifact), exit and save your game. When you start you're game again you'll begin at the save point at the very beginning of the mission. This way you don't have to backtrack on foot and you'll save a lot of ammo too.

An effective, but annoying, way to store your extra stuff is to create an alternate character that is only for holding your extra stuff. Just create a new character, load a co-op game with both your main character and your new level 1 character and give them the items you want to put up. Log back in to your level 1 character and give the items back to your main character when you need them. This can be really useful when you find weapons and items that are above your level, or are saving them to give to a friend's character.

Watch your reload animation. As soon as the cartridge is removed (or rounds are being inserted), click the Right Stick (melee) and the gun will finish reloading. Do this to save time and possibly your life.