Keeping hidden.

Unless the enemy has really good eyesight keeping hidden is really easy. Places to hide/camp are places like up on pipes, in dark corners, behind walls etc.

So if you see any dark places or high places because nobody ever looks up to check who is above them so you can easily hide there.

If you are playing CTF (capture the flag) and you are hiding with the flag it is a really good idea to hide close to where your flag is so when it gets returned it is harder for the enemy to get there before you.