The only thing that I could think of is http://chesstempo.com/
tactics development vs. strategy development

Try studying Jeremy Silman's How to Reassess Your Chess, 4th Ed or, if 658 pages -plus an optional 423 page workbook- are too long for you, study Yasser Seirawans Winning Chess Strategies.
Some middlegame possibilities at various levels:
50 Essential Chess Lessons by Steve Giddins
https://web.archive.org/web/20140708100833/http://www.chesscafe.com/text/review534.pdf
Chess Strategy for Kids by Thomas Engqvist
http://www.gambitbooks.com/pdfs/Chess_Strategy_for_Kids.pdf
Starting Out: Attacking Play by James Plaskett
https://web.archive.org/web/20140708101549/http://www.chesscafe.com/text/review467.pdf
Simple Chess by Michael Stean
https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf
Amateur's Mind by Jeremy Silman
https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf
Winning Chess Strategies
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
Chess Secrets: The Giants of Chess Strategy by Neil McDonald
https://web.archive.org/web/20140708092313/http://www.chesscafe.com/text/review620.pdf
Chess Strategy for Club Players by Herman Grooten
https://web.archive.org/web/20140708101926/http://www.chesscafe.com/text/review696.pdf
Chess Training for Post-beginners by Yaroslav Srokovski
https://web.archive.org/web/20140712013538/http://www.chesscafe.com/text/review945.pdf
Chess Strategy: Move by Move by Adam Hunt
https://web.archive.org/web/20140708093249/http://www.chesscafe.com/text/review890.pdf
How to Reassess Your Chess (4th ed.) by Jeremy Silman
https://web.archive.org/web/20140708095832/http://www.chesscafe.com/text/review769.pdf
Understanding Chess Middlegames by GM John Nunn
https://web.archive.org/web/20140627012322/http://www.chesscafe.com/text/hansen154.pdf
Winning Pawn Structures by GM Alexander Baburin (1998)
https://web.archive.org/web/20140718055446/http://chesscafe.com/text/wps.txt
Understanding Pawn Play in Chess by GM Drazen Marovic (2000)
https://web.archive.org/web/20140708110136/http://www.chesscafe.com/text/review249.pdf
Dynamic Pawn Play in Chess by GM Drazen Marovic (2001)
http://theweekinchess.com/john-watson-reviews/books-of-many-flavours
Winning Chess Middlegames, An Essential Guide to Pawn Structures by GM Ivan Sokolov (2009) https://web.archive.org/web/20140708091955/http://www.chesscafe.com/text/review676.pdf
Pawn Structure Chess by GM Andrew Soltis (2013)
https://web.archive.org/web/20140708101523/http://www.chesscafe.com/text/review908.pdf
Chess Structures - A Grandmaster Guide by GM Mauricio Flores Rios (2015)
"There is also masses of stuff in the book that made me go 'Oooh!' and 'Aaah!' so I think it will have the same effect on you! In particular, I loved Rios' exposition of White's plan of exerting queenside pressure against Hedgehog systems. I'd seen one of the games he quotes in his chapter but I'd never remotely made any link to a structured way of fighting the Hedgehog structure, so this chapter was a real eye-opener for me ... In conclusion, warmly recommended. Lots to learn!" - GM Matthew Sadler
The Power of Pawns by GM Jörg Hickl (2016)
"The didactic concept of the book is admirable. Each chapter defines the structures, explains the typical characteristics and shows the plans for both White and Black. The reader participates by assessing positions and invariably receives useful tips for practical play." - FM Harry Schaack
Python Strategy by Tigran Petrosian
http://sagarteacheschess.blogspot.com/2015/09/python-strategy-book-review.html
Petrosian’s Legacy by Tigran Petrosian (1990)
https://web.archive.org/web/20140708103409/http://www.chesscafe.com/text/review309.pdf
Petrosian: Move by Move by Thomas Engqvist
"Engqvist gives us a rare treat and a genuine, sympathetic understanding of one of chess' greats who nowadays tends to gets lost in the shuffle!" - Michael Ciamarra (2014)
Grandmaster Chess Strategy by Jürgen Kaufeld & Guido Kern
https://web.archive.org/web/20140708093410/http://www.chesscafe.com/text/review812.pdf
so I've been using the tactics trainer a bit, and strongly prefer using tactical openings. I feel my tactics have gotten way better, but I'm not sure about my knowledge of strategy. I want to improve it but don't know how. Should i watch videos (and which ones if yes), try a more positional opening, or something else?
The how to improve begins with knowing what your goal is. Your goal is to add visualization patterns to your brain's memory bank.
There are 4 visualization pattern memory banks:
1. Tactics visualization pattern memory bank
2. Opening visualization pattern memory bank
3. Middle game visualization pattern memory bank
4. Endgame visualization pattern memory bank
Practice each of these 4 every day in order to add more visualization patterns to your brains memory bank.
How:
1.Train with tactics positions
2. Study opening books, videos, etc. with the goal of building an opening repertoire. Know the first 15 moves of 2 openings as White and 2 openings as Black. Practice playing the characteristic positions that result from those 15 moves in actual games, master games, etc.
3. Study opening books, videos, etc, and middlegame books, videos, etc. to familiarize yourself with exactly when exactly the first move of the middlegame is made. Play practice games to become accustomed to and understand the characteristic middlegame positions that arise from your chosen opening repertoire openings.
4. Study endgame books, videos, etc. Learn endgame techniques. Such concepts as the opposition, the queening square, stalemate and self stalemate, Learn the Lucena position, Philidor's position until you can do them in your sleep. Learn the corralling method for the checkmate endgames (K+Q vs. K, K+R vs. K, K+2B vs. K, K+B+N vs. K). Learn about pawn weaknesses (isolated pawn(s), backward pawns, doubled pawns, etc) and how to exploit those weaknesses.
Remember your goal in all of the above training is to add visualization patterns to your brain's memory bank.
so I've been using the tactics trainer a bit, and strongly prefer using tactical openings. I feel my tactics have gotten way better, but I'm not sure about my knowledge of strategy. I want to improve it but don't know how. Should i watch videos (and which ones if yes), try a more positional opening, or something else?
tactics (tactic) development vs. strategies (strategy) development
First we have to define tactic. Then we have to define strategy.
They fit together as follows: All tactics are strategies. But, Not all strategies are tactics.
Tactics are one final goal of strategic planning.
so I've been using the tactics trainer a bit, and strongly prefer using tactical openings. I feel my tactics have gotten way better, but I'm not sure about my knowledge of strategy. I want to improve it but don't know how. Should i watch videos (and which ones if yes), try a more positional opening, or something else?