What chess advice would you now give your younger self??

 Since I'd like to be better, the advice I'd give to my younger self is for the purpose of being a better player.

The general areas are opening, strategy, tactics, and endgames. After the beginner phase (how the pieces moves, opening principals, and basic checkmates), get one good book on each general area and read it.

Play in OTB tournaments even if you don't feel like it. You're never going to feel 100% ready, and everyone has bad tournaments sometimes. Even if you couldn't sleep the night before, or can't seem to focus that day, and even if you lose every game, as long as you put in effort the experience will be one you can learn from, and you'll improve because of it.

Even if a book is frustrating, a little confusing, maybe seems a little too hard, stick with it to the end as long as it got good reviews / is a classic. One for me was Vukovic's Art of Attack. I gave up reading that early, but wish I'd stuck with it. Usually it's not 1 example or 1 idea that's important, it's after spending a month or two on a subject, with many different examples, that ideas start to sink in. Maybe you see 99 confusing examples, but on number 100 things start to click. Also not every part of every book is going to be revolutionary to you. Maybe the last chapter sucked, but don't give up, maybe next chapter will be better for you.

This next one is similar, and is play over GM games even though some moves are totally confusing. Only spend 5-10 minutes on a game at max, and don't try to understand every move. I used to get so frustrated when they sacrificed a pawn (or didn't capture what seemed to be "free" material). If they're frustrating, just ignore those utterly confusing moves. It's like a teen watching professionals play a sport, or a beginning artist looking at master works... it's not that you can copy it tomorrow, but you get a sense for what greatness looks like. Make yourself stop looking at a game after 5-10 minutes! Do a few games a day. Sounds dumb, but like the book thing, it tends to have a cumulative affect, and in the end you do notice things you want to copy and your play improves. This can be modern games, or, as an easy list, just start at the beginning of world chess championship match games (Steinitz vs Zukertort) and go from there slowly working your way to modern times. You'll also see many good openings you might not have known existed.

http://www.chessgames.com/perl/chess.pl?tid=53788

Don't spend 20 minutes on a single tactics puzzle. Obvoiusly you're just trying to brute force guess the solution now, so give up and instead spend that time on reviewing the solution and doing more puzzles. In a real game what happens after very long thinks where you're still confused is you run out of energy due to constant calculation and you make a mistake anyway. At a certain point, even during a real game, it's time to give up on analysis, do a basic blunder check, and just play a move.

However, also a big part of improvement is the ability (or discipline) to do at least a little work every day for years. So a big hint is... keep it fun! Even if you're only interested in improving note that it's better to do something chess related that you enjoy than it is to burn yourself out on things you don't like at all, resulting in long periods of no chess at all.

Don't be lazy, but have fun.  Set goals, but be realistic.  Oh yeah, I would have listened to myself...

Never learn to play the stupid game called 'chess' and stay away from 'chess.com' at any cost.

Don't destroy your brain cells by playing auto-pilot openings like the London System.

That's exactly what the question is asking.

I would have played in the strongest tournaments that I could have entered. That would have been entering Open sections in which there may not have been a prize for my rating range. An example of this would be an Open section that would not have a Best Under 1400. True, I would have had my you know what handed to me on a silver platter but it is said that you learn more from your losses than from your wins. Of course it would have been helpful to have had a really strong player to help analyse these games. Instead, I entered the weakest Swiss sections I could enter hoping to boost my ego by winning a prize that I felt was fairly within reach. Sometimes this idea would work, it usually did not although I still had respectable scores and my USCF rating would slowly go up. I guess that I was afraid of being humiliated in stronger events and I wanted to be, at least on paper, always one of the favorites to win or at least make a damn good run at getting a prize. Of course, I still played in quads which was still good to do but I somewhat regret my Swiss playing strategy. Bottom line: Could have learned a hell of a lot more if my ego had not gotten in the way! 

Don't worry about openings. When I was young, I believed that studying openings would be the quickest way to make me a better player, and I spent an inordinate amount of time trying to memorize theory (most of which I didn't even understand—just parroted it because I believed it was "correct").

Now, I believe that it's one of the least effective ways for a young player to improve. 

I'd tell myself: "Learn the principles of development. That's all you need. If you must study: study tactics. The rest of the time: play games, then review every game afterward to see what you missed."

Stop playing, NOW!

Concentrate on tactics and their patterns.  I was so sure of my intellectual power in my younger days that I thought I should concentrate first of strategy and that I would see the tactics due to strong mental calculation abilities.  It doesn't work that way!

"Study, 9 year old me!"

Don't study Chess Openings.