Urinate cautiously

If you are male, make sure the seat is up, unless you are at a urinal. Be sure both both feet are firmly planted on the ground, and maintain proper balance. Check if the organ in question is outside of your pants - this is crucial! Use both hands to aim. Do not laugh. Avoid distraction and maintain concentration on the task at hand. And never, never bounce a tennis ball during urination!

See also How to Use a Urinal.

If you are female, I can offer no advice

Females, make sure the seat is down (easily forgotten during the middle of the night). In a public restroom (or a private one shared by sloppy people) make sure the seat is dry. Lift any skirts, robes or long shirts; unfasten and pull down any pants, culottes or panties. Sit or squat over the bowl -- don't try leaning over to reach for something.

After urination, wipe off genitalia and put clothing back in place. Wash hands.

This is why women take so long in the bathroom.