1. Only kill a stranger - well over 80% of all murders are committed by a person who knew the victim; stranger murders have the lowest solve rate of violent crimes.
2. Destroy any items that were worn or used before, during or after the murder.
3. Do not keep a souvenir from the murder (for budding serial killers).
4. Always remember Locard’s Transfer Theory - every place you go you will leave something and take something with you, no matter how small. Plan a murder in an incredibly dirty area where finding the small amount you leave would be incredibly difficult - immediately after, remove all clothing (including shoes) before entering any area that can be tied to you (car, home, office, etc).
5. Don’t commit a murder in the first place!!!!
My brother in law recounts this story. Some acquaintance of his asked him how he would commit the perfect murder. He replied, thinking it an intellectual exercise, “I would buy an old shotgun from a pawn shop for cash, shoot the fellow and dump the shotgun far away in a large body of water.”
Later he found out the guy actually followed his advice, shotgun and all. Except he did it in front of 5 or 6 witnesses. I suppose stupidity is a hard obstacle to overcome.
Plausible deniability, I like it..