First I would start by ordering some legal guns. There is no sense in going through all of the trouble of buying black market guns. Also don't forget to get gloves, a gasmask, lockpicking tools, dog repellent, and a knife in case stuff hits the fan and the gun isn't working. Then locate where they life, if they are close, it will be good. Going long distance is a bad idea. Gear up during the night (preferably midnight or whenever the forget they sleep), wear black, and remember to cover your face (bandanna, balaclava, etc). Then when you reach the victim's house, cut off their power. This will prevent them from calling the authorities and/or making you visible in the light. Then start by breaking in through a back door, front doors attract too much attention. Once you've broken in, locate the victim and murder him silently, trying to avoid objects that create noise. If they have a dog, use the dog repellent, and quickly get to the victim. Once the victim is dead, quickly collect shells, cover up your tracks, etc. Once the above is done, find a safehouse to hide in until the heat is off. Find some abandoned building. Once the heat is off, come out and safely live your life. If the cops are getting close to your hiding spot, then keep moving. If you keep moving, you keep them guessing.
I sure hope that helps you.
<3
(I sure hope you guys know that I'm joking.)