Questions about murder

So, I'm planning to kill some people. I just can't tolerate this shit anymore and I have to do something to stop it. I've got all the operational issues worked out, but I'm a bit worried about the psychological consequences of all this, i.e. what is it going to do to my mind? Am I going to go mad with regret and turn myself in because some voice in my head?

Is there anything I can do to prepare myself of what I'm about to do? Should I kill some animals or some old homeless person first to get used to the idea of extinguising life (this is not a time-critical mission I'm on)?