I have the kind of mind that I think would make me ideal to plan murders. I have planned the murders of a few people that I dislike. I wouldn't do it though.
A very important thing to do is to wear clothes that you normally wouldn't wear. When you have dispatched your victim, have a safe place to totally destroy the clothes, even if no visible evidence is on them. That includes your shoes. Bury the ashes.
Make sure you wear gloves (obviously) and something that will stop you depositing hairs at the scene. If at all possible, make the murder scene a place where you would have business being at even if the murder didn't happen. That way if you do leave trace evidence you have an excuse.
Although you want to not be seen at all, make sure you can leave the immediate scene in disguise.
Maybe your disguise could include a large beard and sunglasses. But if you do so, it could also be a good idea to have a second disguise on underneath to fool people. For example, if you wear a black beard have some red hair showing from underneath. That way any witness will think they have some vital clue and it will totally throw off the police. (assuming you aren't a redhead).
Any murder weapon must be disposed of. It doesn't matter if its your favourite nickle plated pistol, it MUST be wiped down and placed where it will never be found. It is best if this is the kind of place that won't be built on in the future. If your weapon is burnable, burn it.
But you shouldn't be using your favourite nickle plated pistol as chances are that someone saw you with it.
I wouldn't even attempt to dispose of the body. Too easy to get caught. Bodies are VERY hard to dispose of completely.
Work alone. Its not a good idea to have anyone else know your plans, no matter how loyal they are. Things can happen down the line that might make them either turn against you or reveal something by accident.
Damn, that was hard to type with my nose. *wipes drool from chin onto shoulder of straight jacket*