The achievement requires you getting to level 40 in MyGM. Getting level 40 requires around 480,000 XP, and you don't really get a lot of XP playing normally. This was the fastest method I found:
To start go to MyGM(not MyLeague) and start a new file, and do the following
-Pick
Unranked-Pick Easy(probably doesn't matter)
-Pick any Team you want.
-Upon entering the Calendar, hit
and hold
till you get to options.
-Select MyGM Settings
-Turn
Off Pre/Post Action Dialog, and
Give 10 extra actions per day.
-Go to Trade Sliders
-Turn
OFF Recently Signed Restriction, Financial Trade Rules, Stepien Rule. Turn
ON Trade Override (
Don't turn off Trade Logic, or you won't get any Exp at all.)
Now that we got everything prepped, go to the Front office tab and go to Propose Trade.
-Trade
your Teams 2nd round pick for the 76ers 1st Round Pick(or whatever team pops up first)
-It will ask you if you want to Override the trade, say yes.
-You get 500 XP for this
-Go back to Propose Trade
-This time,
trade the 1st round pick back for the 2nd round pick to the same team.
-This gives you around 130 XP
-Repeat this process until you get to level 40.
You could go around to every team an trade for their 1st round pick, but you'll end up doing this method anyway, because you'll run out of 1st round picks to trade for.