I think mentoring with a string of exi's for several weeks is a great way to upgrade the level of a player.
As a player that has upgraded over the past year, I can only attest to what made me better:
Take the WORST goalie you can as OFTEN as you can. Change your offense at least two or three times. In GENERAL, if you are a B player, your "old habits" are the wrong ones && your goalie play is not high enough. Using bad goalies forces you to use manual more often and forces you to adjust when & how you do that.
Having played some 2v2 back when it was played (not heavily, but enough), I recognize when I play Habs where I see a manual save I feel he learned in 2v2. It's weird, you can almost sense that was a crazy move he learned doing on 2v2. SO, more experience can lead to higher level of play, but it also takes time to absorb what you have learned.
FOR ME, the biggest jump came when I gave up on "old me" being good enough. So, I don't play drunk! In addition, I was playing good for about a month, and came across AJ. He just beat the shite out of me, like 8-1. After a few beat downs, he told me I was trying TOO hard to get perfect shots and not getting enough SHOTS up.
That's when I realized I needed to tweak how I play more than a little on offense. My defense was always decent. I upgraded my goalie play, and changed my offense and it's shown over the past 2-3 months.
So, playing vs A+ guys willing to give criticism and being will to ask HELPS. Being willing to adjust your game is a must if you plan on going from B to A.