Remember to ward, call mias and don't rage.
Besides that have a small pool of champions to use, dont go 10+ range of selection, have 4 or 5, so you can get better at them.
If you're jungler remember jungle timers: red&blue 5 min, dragon 6 min and baron 7 mins (you might want to assure that).
Keep a cool head, if you're calm there's a higher chance you can outplay someone if you aren't pissed or raging hard.
And always ward around, even if you're the adc or something like that, remember that is everyone's job to ward around, not only support, he should ward more than the others tho.
Remember that midgame is about adc farming and mid,jungler and top having higher prescense in teamfights.
If you're going to be is just about position, farm and knowing when can you negate farm and how.
well good luck.