Think of the car as a tennis ball, doesn't matter which way you tilt the trailer (forward, backward, side) the tennis ball should not be able to move. Don't take any notice of how a tow truck operater secures a vehicle, 98% of them should be shot for their unsafe practices (a winch + 1 wheel tied down is not safe).
The easiest way is as Rekin has posted, using each wheel diagonally to the corner of the trailer. This prevents forward, backward and side movement but can play havoc on alignments.
Use 'hooker & keeper' 50mm ratchets which you can get a 4 pack from bunnings for about $50 rated to 1-2 ton. The amount of retards I see at motorsport events use 1x 20mm s-hook looped through the front axle and another looped through the back axle is astonishing. Most importantly is to tie it all down, then do a lap of the trailer to re-check each point then drive the car 50 or 100m and brake then get out and check it all again.