Is there a guide somewhere that explains how what affects development in this game? I could use real-world lessons, but I'd rather know what's actually helpful/detrimental (and what EA hasn't taken into account).
I can only speak from experience within the game (Be a GM was pretty much all I've played), so take what I say with a grain of salt, even though what I've just said before is most likely the case (and I've tested that over about 50 seasons of Be a GM for sure.)
-Playtime is definitely a factor (players get more experience playing more minutes on the 1st line/powerplay/pk)
-How successful the team/player is: a team-win gives more experience than a team-loss, and making the playoffs and being successful in it is even better. (aka If you win the Calder Cup with a Rookie on your first line, he'll get heaps of experience)
-Natural Development, just how likely the player itself is to develop, this is partially indicated by the colour&amount of stars
-Injuries, if your player is injured he not only misses playtime, but he will also risk just losing some development potential in general
These are factors that I'm fairly sure about play a role. I am NOT sure how much their "team-likeness", as in, how much they like your team (you're successful, you have a lot of their countrymen, you gave them good contracts, etc) plays a role, so I don't want to speculate on that too much.
And obviously, there's also some good old random luck involved.
Overall, it's a LOT like you "feel like it should be", with the random "EA factor" in it. If that helps. There's probably way more detailed guides out there with actual numbers behind it, but I figured I'd give it a shot.
EDIT: Oh, also: Don't put too much pressure on rookies. If you put a 75 Skill rookie on your first line NHL and he keeps getting crushed (stats-wise, hits against him, negative +-, etc), he WON'T develop well. That's one of the reasons I don't sign Rookies until I know they're fit for the AHL. I rather have them be happy and get good stats in the Juniors than get terrible ratings in the AHL, because they won't develop well.