I'm also a pretty good player, so I'll give you a little advice: use special memory training apps to improve your calculations, and learn the openings, as this will greatly affect the start of the game.
don't shenk your pieces away
you don't need to be titled or sth to
know the worst errors that beginners make
don't learn openings by heart but understand that all pieces want to take part in the game working together as a team ( and don't attack with queen + one knight or bishop only )
"... I am not a big fan of weaker players memorizing lots of opening lines they will never play. However, it is quite a different issue to spend a small amount of time learning how to play your openings a little better each time they occur. A long journey begins with a single step. ..." - NM Dan Heisman (2005)
https://web.archive.org/web/20140627023809/http://www.chesscafe.com/text/heisman50.pdf
"... Overall, I would advise most players to stick to a fairly limited range of openings, and not to worry about learning too much by heart. ... the average player only needs to know a limited amount about the openings he plays. Providing he understands the main aims of the opening, a few typical plans and a handful of basic variations, that is enough. ..." - FM Steve Giddins (2008)
@weo2 said in #1:
> I'm also a pretty good player
We have only your word for it.