By the time you master all of the early job tiers, you should be around level 60 or so. You'll have access to both the Capo and Consigliere jobs tiers. The Capo job tier really sucks.. most of the jobs don't give many experience points considering their energy cost. To make matters worse, as you are leveling up, you need more experience points per energy point to level up. However, there is hope! Most of the Consigliere jobs are very energy efficient. That is why I recommend mastering both tiers at the same time. Jobs like "Steal an Arms Shipment" in the Consigliere tree have a good experience points to energy cost ratio, but most Capo jobs like "Loot the Police Impound Lot" have a poor exp / energy ratio. For example:
You have 750 energy and need 1250 xp to level up. You'll do "Steal an Arms Shipment" 10 times, and you'll have 400 energy or so left and 500 xp to next level. This will allow you to do the "Loot the Police Impound Lot" 7 or 8 times and still level up. That way, you'll master the hard jobs without ever having to wait for energy regen!
Cell Phones, Illegal Transaction Records, and Blackmail Photos
These are the real roadblocks of this level. If you are able to stretch your energy out well, you'll have no problem mastering off all the jobs prior to these. The "Steal Bank Records" job pays out pretty well, so Illegal Transaction Records should not be a terrible roadblock. However, getting all those cell phones can be tough. Now if you have been following the guide to a T, or if you just need some cell phones, now is the time to use your Energy Pack to load up on Cell Phones and Cameras. Additionally, if you have any leftover energy after doing efficient jobs that is about to go to waste due to an imminent level, use it on the "Rob an Electronics Store" job. You can never get enough of these consumable items!
Be sure to use all your stamina every level; there is a chance for these consumable item drops to be found during fights!
However, even using the energy pack strategy, you may find yourself short on cell phones when it comes to master jobs like "Flip a Snitch" for the second or third time. However, by the time you master all the other jobs, you should be closing in on level 100. At this point, it is a good idea to start branching out to the Underboss tier. While mastering efficient jobs in the Underboss tier, you can use the extra energy to rob the electronics stores to collect more phones. By the time you master Capo, but before you master Consigliere, odds are you will have much of the "Boss" tier unlocked as well. I think it is most efficient if you work on all 3 or 4 tiers at the same time. That way, you can simply just rob the electronics store when you have an energy pack. However, if you have a few hours to sit down and play on a lazy sunday and want to go level 100-200 in one sitting, you'll have to budget energy to rob the electronics store enough to collect these items. Just make sure you budget your energy right- if you end up short on exp, you'll have to stop playing for awhile until you have enough energy to level!