Well if you plan on doing it yourself
1) make it look like suicide, (check medical dictionaries)
2) DNA - make sure that you are covered completely so none of your DNA is present
3) Location Location Location - pick a spot away from police like small town, forest etc
4) DO NOT hide the crime, but hide the connection to the crime
5) Gun - make sure no powder etc is on you but mostly find the bullet
6) Alibi - is essential, book hotel with no camera's out of town etc.
7) Media - avoid watching media etc since cops try mental games to get you to admit
8) Don't google etc - cops will look at your computer to check shit like that out
9) Keep your relationship positive, cops love motives - don't give them one
10) If all else fails, inject air into their veins and this will stop the heart
11) Insulin in veins will do the same thing, over 1200 units
12) Brush up on your forensic skills - murderers learned a great deal from CSI
13) As little clean up as possible