Low Gravity
Lowering gravity will result in higher jumping and taking less damage from a fall. To lower gravity, enter "sv_cheats 1" into the console and then type "sv_gravity" (insert a number). The default gravity is 800. The amount of time in the air increases as the gravity lowers. Also, everyone is affected by it. This means that you or your opponents are stuck helpless in the air until you reach the ground. If the gravity is lowered to 0, no one will fall down after jumping. You can take advantage of this, but be careful not to jump, or your enemies will use it against you. Lower the gravity to reach higher places that your enemies will not normally check.
Noclip
Noclip allows players to walk through any solid object including floors and ceilings. To enable noclip, enter "sv_cheats 1" into the console. Then, put in "noclip 1." Doing this will only affect you. There is a fixed speed for noclip, about the same speed as running, and it decreases accuracy. Use Noclip to sneak around the map or pop out of a wall when an opposing player gets close.
God Mode
In God Mode, your health rate will not lower when you take damage. To activate, enter "sv_cheats 1" and enter "god." The only way you can lose the round is if time runs out or if the opposing team somehow completes the objective. God Mode is useful if you want to make a match where it is you versus the maximum number of bots on the other team, set at the hardest difficulty. Don't use God Mode when playing with friends because there is no way to counter it and the game won't be fun. However, combining this with NoClip and stalking your friends can provide a few laughs.