Best piece of advice I can give for those trying to up their game is one I still find myself struggling with. It's important but, oh so hard to follow:
Don't try to
bluff a calling station.
Sounds simple and basic. But I can't tell you how often, Everytime is sit down to play, I make those stupid mistake. It's butal, and its a hell of a leak that I have yet to fully plug.
As for preflop charts. That's just simple memorization. Grab a chart you believe to be accurate, and make some flash cards. You'll have it down in a few weeks at most. They next level is knowing when to bluff - so this involves learning opponent play styles, and their opening ranges. Level three is studying GTO and Is the ultimate in preflop game improvement. And that involves hand strength, chips on the table, chips in stacks, position in the tournament, etc. It's way more involved and takes years to learn.