Always look behind you before moving. Enemies can and will sneak behind your back. You can be swarmed from behind and abruptly killed.

Aim for visor kills when low on health. If you are low, keeping a distance should already be reasonable. Try to practice your aim to get visor kills.

Run diagonally to move faster. This will allow you to move 1.4x (the more accurate number is √2) as fast.

Jump. Enemies can't reach you while you are midair, and enemies cannot jump.

Turn around. Enemies don't turn very fast. This can allow you to briefly avoid being chased.

Allow enemies to turn to you. This will allow you to get visor kills more easily.

Spawn camp enemies. Prepare to shoot enemies before they spawn.

Gather the horde. You can kill multiple enemies at once.