I'm not going to bore you with all the complexities within money management as there are thousands of references online that go into detail of all the various aspects pertaining to this subject although it is just as; if not more, important than actually picking winners. Suffice it to say, my belief is never wager more than 3% of your total bankroll on any 1 play.
You must have a bankroll used strictly for your betting. Do not use money that could be used to pay bills, rent, etc. for betting.
Make your wager amounts proportionate to your current bankroll on every play.
You'll never see 5 star specials, locks of the month, plays of the year or any other garbage like that on this site.
I recently changed my betting philosophy to bet to risk, not to win. Simply put, my unit size is now based on a flat 1 unit or a $100 bet regardless of the juice unless otherwise specified. I will make it clear if I'm recommending more units. I did this because I was losing way too much juice when betting to win. Of course I realize the win amounts will be less but I should be better off in the long run and it allows me to play higher priced money lines at much less bankroll risk. Feel free to follow your own judgment in regards to how you wish to handle your bet amounts.
One more very important note is to never bet NFL double digit favorites because the league is far too competitive. You can get away with laying high spreads in just about any other sport (CFB in particular) but I guarantee you'll save yourself many losses abiding by this rule.