Right Hand Rule

1. Point your index finger (and your middle finger) along the direction of motion of the charge v. For a current carrying wire this would be along the direction of positive current flow.
2. Rotate your middle finger away from your index finger by the angle q between v and B.
3. Pivot your wrist about the direction of v until your middle finger is pointing along the direction of the magnetic field B.
4. Hold your thumb perpendicular to the plane formed by both your index finger and middle finger.
5. Your thumb will then point in the direction of the force F if the charge q is positive. For q < 0, the direction of the force is opposite your thumb - alternately you could use your left hand for negative charges.