Best way to formulate a plan?
Opening Principles:
1. Control the center squares – d4-e4-d5-e5
2. Develop your minor pieces toward the center – piece activity is the key
3. Castle
4. Connect your rooks
Tactics...tactics...tactics...
Pre Move Checklist:
1. Make sure all your pieces are safe.
2. Look for forcing move: Checks, captures, threats. You want to look at ALL forcing moves (even the bad ones) this will force you look at, and see the entire board.
3. If there are no forcing moves, you then want to remove any of your opponent’s pieces from your side of the board.
4. If your opponent doesn’t have any of his pieces on your side of the board, then you want to improve the position of your least active piece.
5. After each move by your opponent, ask yourself: "What is my opponent trying to do?"
Middlegame Planning:
1. Expand your position:
a. Gain more space.
b. Improve the position of your pieces.
2. Decide on what side of the board to play.
a. Queenside: a-c files.
b. Center: d-e files.
c. Kingside: f-h files.
Compare, space, material, and weakness(es)
Play where you have the advantage.
3. DO NOT HURRY. Regroup your pieces, and be patient.
Middlegame Planning:
1. Expand your position:
a. Gain more space.
b. Improve the position of your pieces.
2. Decide on what side of the board to play.
a. Queenside: a-c files.
b. Center: d-e files.
c. Kingside: f-h files.
Compare, space, material, and weakness(es)
Play where you have the advantage.
3. DO NOT HURRY. Regroup your pieces, and be patient.
Possibly helpful:
Simple Attacking Plans by Fred Wilson (2012)
https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf
http://dev.jeremysilman.com/shop/pc/Simple-Attacking-Plans-77p3731.htm
Logical Chess: Move by Move by Irving Chernev (1957)
https://web.archive.org/web/20140708104437/http://www.chesscafe.com/text/logichess.pdf
The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)
https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/
Seirawan stuff:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
http://www.nystar.com/tamarkin/review1.htm
50 Essential Chess Lessons by Steve Giddins
https://web.archive.org/web/20140708100833/http://www.chesscafe.com/text/review534.pdf
http://www.gambitbooks.com/pdfs/50_Essential_Chess_Lessons.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
Chess for Hawks
https://www.newinchess.com/media/wysiwyg/product_pdf/9041.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
Chess Strategy for Club Players by Herman Grooten
https://web.archive.org/web/20140708101926/http://www.chesscafe.com/text/review696.pdf
Pawn Structure Chess by GM Andrew Soltis (2013)
https://web.archive.org/web/20140708101523/http://www.chesscafe.com/text/review908.pdf
The Power of Pawns by GM Jörg Hickl (2016)
https://chessbookreviews.wordpress.com/tag/the-power-of-pawns/
https://www.newinchess.com/media/wysiwyg/product_pdf/9034.pdf
Most of the comments here revolve around planning for the next move or so by looking for tactics/combinations. For longer term plans, I love the following two books, especially Wilson's book. Following a simple plan like, "If possible, point all your pieces at your opponent's king," gives you an overall guide to how you make your moves so your pieces work together.
Fred Wilson, Simple Attacking Plans – four straightforward principles demonstrated with 36 annotated games.
Michael Song and Razvan Preotu, The Chess Attacker’s Handbook, fourteen principles demonstrated by games and with example problems.