Where should I start? So, I am returning to chess after not playing for about 10 years. I learned the basic rules when I was in elementary school and then didn't play for a while. I am starting to get back into chess and am wondering where I should start.

Just for reference here is what I know:


How to set up the board
How the pieces move
How Castling works
How Check/Checkmate works
Other basic rules needed to play at a beginner level
I've been a "life-long beginner" - my USCF rating hovered around 900 for years and years, and just playing OTB chess wasn't helping to improve my ability because I was losing almost every game, for years (though usually against players rated much higher than me, so it didn't affect my rating much).  It was a long time before I made even a minimal plan to actually improve - so my situation is/was not totally different from yours.  I can't tell you what's best for you.  What I can tell you is what worked for me:


Watching chess classes on YouTube.  The Saint Louis Chess Club has some amazing classes on YouTube.  There was a series of classes called "Beginner Breakdown" that was incredibly helpful for me.  It mainly consists of looking at novice level games - games that have situations that you or I could conceivably get into - and seeing what mistakes were made (and what should have been done instead).  GM Ben Finegold also did a series of kids' classes while he was a GM In Residence at the Club, I found those extremely helpful as well, for the same reasons.  And both of these series are actually entertaining as well as informative, so they kept me engaged very effectively.  Don't feel funny about consuming instructional materials aimed at kids.  It's about level of chess ability, not age (and I know many of the kids that were in these classes when they were recorded were probably rated higher I was).  I can also tell you that the chess instructional videos on YouTube that are the least effective for me are the ones where the "video" is just a screencast of playing through games using Chessbase or something, with an unseen narrator describing the game.
Tactics, tactics, tactics...  Find novice to intermediate level tactics problems and work them.  A lot of them.  On a daily basis.  I worked through all of the problems in the "Tactics Time" books by Tim Brennan and Anthea Carson.  These books were great because they are tactics studies from novice to intermediate level games.  They are not studies from grandmaster games where you have to calculate ahead 6 or 8 moves to see the solution, they're problems from games played by people at "our level", and situations like what we might face - and they're solvable by people at our level of ability.  Going through these books is even easier and more convenient if you get the Kindle versions, and you can work through a couple of problems at a time while waiting in line at the store, riding on the train, or whatever.  Also, the Lichess site / app is a fabulous never-ending source of tactics studies, and I also find that they're easily consumable by novice to intermediate level players, and with the app on a mobile phone you can do a couple of studies at a time, anywhere you happen to be.


This was (and still is) really my whole study plan.  Just doing these two things (and playing OTB chess in tournaments when I have the chance), I (finally!) was able to pull my USCF rating up by about 200 points in the space of a year or so, and my "Training" rating on Lichess is now over 1700 (though how that might correspond to actual play - if it even corresponds at all - is difficult to say).