The right-hand grip rule of electromagnetism
If you put the thumb of your right hand in the direction of the current flow and encircle the wire with your fingers, as shown below, the direction of those fingers will correspond to the direction of the magnetic field.
NOTE: The direction of the magnetic field can be verified by plotting a compass needle point around the wire.
To remember that you use your right hand and not your left, remember the following mnemonic:
GRIP IS RIGHT HAND ON A WIRE
All the R's go together.