(Don't actually kill anyone...please...)
1. Wear a hair net or balaclava or something, it'll keep your hair from getting in the scene.
2. LOOK AT THE GROUND SO THEY CAN'T SEE YOUR FACE ON THE CAMERAS
3. Dye and cut your hair after the murder so they can't put it to your name.
4. Do it at night
5. Wear all black (I do that anyway tho sooo...)
6. Use a weapon that you can burn or nobody will suspect (e.g. A pillow because you can burn it or a local fountain to drown them.
7. Wear gloves so you don't get your DNA on the body.
8. If they scratch you, clean their nails so there isn't any DNA there.
9. Bring a spare outfit to change into after burning your black one.
10. Sunglasses over balaclavas are very helpful
11. If things get public, move out of the country ASAP (if you leave it too long, they won't let you out.), change your name and change your appearance.
12. Don't make it dramatic...try to minimize the amount of blood they loose.
And that's how to kill somebody and not get caught.