so ECF 87 is roughly 1700 Fide? This is a very common place to get stuck. I had similar problems around 1750 - spent a year with no improvement. I took a break came back fresh, and then evaluated what my weaknesses were with a fresh perspective.
As far as methods of improvement- the things that have worked best for me
1) go over my own games
2) study master games
3) deepen my opening understanding
4) study the endgames and middlegame configurations that come up the most in my openings
5) tactics problems
there is nothing new int this but the specifics might be worthwhile to discuss.
1) This doesn't mean plug in the moves the night after the game into chessbase with fritz on. I go through the next day and record all my thoughts, lines I considered etc. Then I take it to an IM who goes over it with me. We spend 30min to an hour per game depending on what things I missed etc. Lastly, after a couple months I go back and re-annotate them. This is helpful to see things with fresh eyes. I often find thematic flaws over a group of games that I might dismiss if I just looked at the game after I played it.
2) Solitaire method. I give myself 5min per move and I record all the variations I calculate. I compare my lines to the annotations so it's important to stick to games that are well annotated. Frequently, I choos the right move, but I didn't consider or calculate deeply enough to justify the move.
I also do stoyko exercises- I think I get more out of this than studying tactics. 15min, I take critical middlegame positions and I calculate it out as deeply as I can.
lastly, I collect interesting positions and ideas in a seperate chessbase folder.
3) I went to an IM discussed my openings, collectively we changed some of them to better suit my style of play. Once I had settled on the specifc variations, I plugged them into CPT. As I play blitz or CC I add new lines that I play, including bad lines so I can save up the refutations. I then go through and drill my openings about once a week or so. I also keep track of what is played against me OTB and allot the proper % of time based on what I see the most. I.e. I spend more time studying the c3 alapin in the Sicilian than I do my intended main defense since the vast majority of my opponents play that.
4) This could just be included under opening prep. I look at the most common endgames i.e. do I frequently get the bishop pair vs closed center, knight vs bishop etc. I and study them based on what I am most likely to see.
Likewise for middlegame I work on pawn structures. Do I play with or against the IQP? etc.
5) I do chesstempo.com, shredder puzzles on my phone and have a couple books I drag around.