When I was a new driver I almost learned the hard way how important it was to turn the wheels properly to park safely on a hill. I had parked my father's truck on a hill, didn't put it in park, didn't set the parking brake and kept the front wheels straight before getting out and walking away. Fortunately for me, a friend saw the truck start to roll away and yelled at me. I was able to jump back in and do what I was supposed to have done before I left the driver's seat.
If you are parking on a hill without a curb at the edge, turn the wheels to the right. When a curb is present, turn the wheels to the right if you are facing downhill and to the left if you are facing uphill. If the vehicle does roll, the contact with the curb or turning to roll across the hill may prevent a runaway.
Always set your parking brake, even if you are not parking on a hill. Put an automatic transmission gear selector in Park, or if your vehicle has a manual transmission, put it in reverse if you are facing downhill or first if you are facing uphill or on a level surface. The combination will make it almost impossible for the vehicle to roll away.
Finally, don't forget that you must park within 30 centimeters or 12 inches of the curb.