Most Wanted Achievement
Reach reputation level 100.
Approximately 23,336,416 (23.3 million) XP is required for level 100.
The more stars, the higher the payout. The White Stars on a job = the base payout for completing it. The Gold Stars on a job = the difficulty and are a multiplier for the payout.
Investing in the Faster Learner skill (Mastermind tree) early on will help. Acing it and playing with others who have it aced will make it even better.
The Ukrainian Job and the Night Club are both fairly quick jobs and have the highest potential payouts in terms of XP/minute.
The quickest way to boost XP is to find a non-Pro Rats job with as many stars as possible in Crime.net Offline (you can get 100k XP on a maxed out Rats job but the one worth 40-50K is easier to find). During day 1, blow up the lab, on day 2 find the info (burned or not) and once day 3 starts, sprint to the bus, kill all the rats on board, and then sprint back to the escape chopper.
Day 3 will take you roughly a minute. Once you have picked a card, instead of proceeding to the menu, pause the game, and restart the job. This will allow you to replay Day 3 only and get the big end of job payday as many times as you like. Using this method you can go from level 50 to 100 in roughly 25 hours.