Assuming you know how to go infamous (if you don't know read TehMeatyWalrus solution for
Becoming Infamous), all you really need to know is how to level up fast to infamy 10 times as quickly as possible. I'd advise deploying 2 techniques:
1) Stealth bonus heist + infinite heist + crime spree combo
2) High xp infamy rewards
When you complete a heist in stealth, you'll get an xp stealth bonus in your next heist (Loud or stealth). For
Bank Heist: Gold the bonus is 10%. Then take that bonus to an infinite hesit (a heist that let's you collect as many bags as you want) like
Cook Off and use this calculator by Rodoto to figure out exactly how many bags you need to level up as much as you need for level 100.
https://steamcommunity.com/sharedfiles/filedetails/?id=22920... Once finished with the heist and at level 100 do a decently long crime spree (which allows you to bank xp and other rewards) before you infamy. Once you infamy cash in your crime spree xp so you can build back up a decent class to rinse and repeat.
When you infamy be very careful which reward you pick as some increase experience more than others.
More XP rewards will increase xp gained by 10%, while specific rewards like
Balaclava only increase xp gained by 7.5%. The 2.5% difference seems trivial now, but when you need millions of xp and have to play
Cook Off for three to four hours straight, you'll notice how much it adds up.