Why murder? This question will have as many answers as there are people murdered and those doing the murdering. In a sense, the question of why is beside the point. What’s important is that one has decided, for r(more)easons sufficiently compelling, to take the life of another.
Pick your target. Anyone will do. Circumstances will usually dictate the choice of victim. Better to not pick a child, though, as its killing will elicit universal outrage, and if you’re caught and sentenced for it, your time in lockup will be that much worse. Child killers do not fare well in prison.
Pick your method. Guns are traceable. Knives are bloody and too, too intimate. Poison is good, but requires an often elaborate amount of planning. Pushing someone off a height is perhaps the cleanest method, but hardest to set up. Do not research things on the internet, as this can be traced back to you. Play out different scenarios in your head until you arrive at a satisfactory plan. Consider the steps carefully, then try to imagine the different ways law enforcement will approach the crime based on the method you have employed.
Prepare, prepare, prepare! Do your homework. Study the habits of the victim. Know their comings and goings. When will they be alone? When do they go to sleep? How far do they drive to work? Commit all details to memory. Know the victim as well as they know themselves.
Keep your pants on! Cultivate a mental sense of cool to serve as an emotional bulwark behind which you can hide your feelings. Betray no thoughts that might give you away. After all, you re no killer! If you believe this fervently, and prepare throughly, you will not get(less)