Guide to the TF2 PROPHUNT mod
 

If you're a big prop, like planks, then try to hide yourself with similar real props.
If you're a control point, get as high as possible, you can't be seen from below.
If you're a small prop, then do NOT stay on the ground, either get on something (if your TV, get on a cart, etc) or get onto a roof, or fence, or something.
More to be added once I'm not lazy.