Like someone else said earlier, don't worry about stats, just play your best.
Now for my discussion, I believe that trying HARD and being LOGICAL, REASONABLE, and LACK OF RAGE helps out a lot for stats.
1. You don't want to stat whore and lose at the sake of it. Your team will hate you, which will cause RAGE which will cause TROLLS which will cause YOU TO TROLL and RAGE.
I suggest typing rather than using the microphone to discuss out problems and if you really have to, pause the game and talk it out.
*I am aware that no matter how mature of a person you are, a true troll will be a troll so just /ignore add IGN and mute and play your game based on your style and really REALLY focus. Play according to yourself.
Don't judge other peoples gameplay, rather, focus only on yours and how you could have been the game changer that wins them the game (whether the retarded trolls acknowledge it or not).
That is my personal outlook on it.
As for actually getting better better (in the aspect of skill rather than keeping cool), you have to have good mouse movement. Invest in a good mouse with a sensitivity that allows you to be flexible. Always use hotkeys, know the basics such as roles and wards and couriers (pretty much the common sense of HoN in which people know but refuse to do because they're super noob, super selfish, or super troll).
If you want feel free to message me on d2jsp for my IGN('s) and I could give you a run down on how to play well. It takes practice and knowledge. Knowledge is half the bottle and out thinking your opponent is important in outplaying them. (basic mind game concepts)
Cheers
-JaySongs