A big thing to avoid when pulling a trailer is what is called "jackknifing." Named for the position of the vehicle and trailer, this is most common when backing up with a trailer.
It is basically a situation where the angle between the vehicle and the trailer it is pulling is less than 90 degrees, or beyond an L shape to a V shape.
Avoid this by never letting the trailer position get beyond the L shape. When reversing with a trailer, just take it slow and get a feel for the trailer. Keep your movement of the steering wheel to a minimum, and remember, you can pull forward to straighten out, so if you are struggling, just start over. Jackknifing will damage the hitch and trailer, so be aware of it.