What's a good study plan for 1800+ rapid?

Hi there! I'm an intermediate player, simply trying to improve. I reached 1800 rapid just a few days ago, and I have the long-term goal of NM (and short-term goal of reaching 2000 rapid by the end of the year). Most study materials I've seen recommended are geared towards beginners and such, so I was wondering if anyone here has any materials for my rating. Opening repertoires aren't an issue. Thanks!

Pawn structures

While I appreciate you taking time to reply, I was specifically inquiring into specific recommended materials to look through rather than general concepts.

Getting opening/endgame courses that you are interested in on Chessable has really helped me and doing lots of puzzles, including the most "basic" ones like mate in 1.

Rock Solid Chess a great book

By Sergei Tiviakov? I thought that wasn't out until April?

New In Chess has it.

My bad, I’d recommend chess structures by Mauricio Flores Rios.

1. Identify your biggest weaknesses.

2. Work on improving those weaknesses until they are strengths.

3. Rinse and repeat.

There is not a single "study plan" for players once they have gone beyond the novice level because it will depend on what you need to work on.  Presumably, your tactical vision is decent, but you may need to work on endgames, or positional play, or openings, or converting advantages, or resourcefulness, or all of the above, etc.

I have that book also but Rock Solid Chess is a great book. It's fun, interesting and worthy of being studied.

Endgame Challenge (Chess Problems and Studies) by John Nunn
Chess Endgame Training by Bernd Rosen 

Chess Training for Post-Beginners by Yaroslav Srokovs

Test Your Chess IQ: First Challenge –by August Livshitz

Can You Be a Positional Chess Genius – by Angus Dunnington

Thanks for taking the time to suggest all these materials, everyone! I'll make sure to check all these out.

Pawn Power in Chess by Hans Kmoch.

That book must have added HUNDREDS of points to my playing strength... although I had to read and re-read it a few times before I could really absorb it all.

Also, read all my posts in the first couple of pages of this thread, and play over the annotated games paying attention to the notes.

GM Larry Evans' method of static analysis - Chess Forums - Chess.com

A lot and a lot of practice through slow-play, heavy self-analysis of each and every game, as well as practicing visualization and piece interaction. You can get up to about 1300-1400 by simply bringing up your performance floor (eliminating the clear tactical and positional blunders). From there, I myself left that little rating slump by refining my understanding of concepts like square weaknesses, color complexes, and piece improvement, and that yielded good results for me. It may not be the same with you, but I hope this helped nonetheless.

See my edit just above.

I find a lot of success from my recent library. I live in a relative small town in northern Sweden of around 100 thousand players without a larger library, but there is still a handful of - while old, well written and well describing books. 

I found most success and development from Jacob Aagaard's "Attacking Manual 1". It brings forth a lot of positions which trained my pattern recognition and tactics to implement. 

Although reading isn't for everyone, but what made me improve was certainly book learning. I've found that a lot of videos lack self input, you kind of just sit there watching the producer doing their thing without actually getting to experiment. That's why just sitting at my board following the book's examples helped me improve so much.

Anything other than a book about it where I dont have to pay but can still learn?

Don't you think that as you approach expert level that it would be somewhat unrealistic to have efficient study methods that don't require you to pay? I mean, you can always look up a pdf of the book, but... 

You get what you pay for.