Old School Mode
Old school mode enables higher jumping for your character, allowing you to get to hard to reach places much easier. Switch to old school mode under "Game Rules" in the "Game Setup" menu.
Techniques
Here are a few techniques to be mastered. These will help you in both standard and old school game modes.
Running jump: This allows you to jump farther and higher than a standard jump. From a standstill, a single running step gives a length and height advantage to your jump.
Jump and crouch: On certain maps, you may need to fit through a small hole that is above your character is. From a standstill or a running start, jump and immediately crouch in mid air, aiming for the desired opening.
Double jump: A single jump may bring you to a ledge or fixture that you slide off of. When you make contact after your initial jump, immediately jump again. This will put you farther up on the ledge, where you can stand.
Rocket jump: This advanced technique adds height to your standard and old school jumps. From a standing position, find the place you will jump to and get lined up so that it is directly behind you or to your side. Aim down and in front of you. Jump and fire an RPG, or rocket propelled grenade, at the same time. The recoil will propel you higher toward your goal. Also use this to extend your long jump, by firing at the ground while in the air.
Partner jump: Have a teammate help you by being a step for you to jump from. For a little height, stand on their prone body. To get higher, do a double jump from their crouched or standing position.
Environment
Whether you are trying to reach a rooftop or go outside the map, all glitches involve going up first. Get on top of walls and run along them. Jump from high places to the tops of utility poles and trees. Use ledges, awnings, rails and wood sticking out from damaged buildings to get where you are trying to go. Nearly all visible structures have a space to walk or stand on. Invisible walkways also exist. You can find them by exploring, or by seeing other players standing in midair. Be aware of your environment and learn to see opportunities.
Practice
Start a private match, set it to old school mode with unlimited lives and no time limit. Choose a map and play it alone. Try to get to the highest points and jump to other places. New discoveries can still be made, and well-known glitches should be practiced so they can be executed in the heat of combat. Your first step to a great glitch could be as obvious as a blocked staircase, or as unassuming as an old washing machine amid the battlefield rubble.