Restarting Chess
"..., you have to make a decision: have tons of fun playing blitz (without learning much), or be serious and play with longer time controls so you can actually think.
One isn’t better than another. Having fun playing bullet is great stuff, while 3-0 and 5-0 are also ways to get your pulse pounding and blood pressure leaping off the charts. But will you become a good player? Most likely not.
Of course, you can do both (long and fast games), ..." - IM Jeremy Silman (June 9, 2016)
https://www.chess.com/article/view/longer-time-controls-are-more-instructive

I stopped playing for a few years and I started again and I suck lol. I don't know where to start playing again, but I've been playing a lot of blitz on here and I'm always missing obvious combinations and moves.
Should I refine my positional awareness or should I change my opening repertoire? Right now I don't have many preferred openings but I aim to play the centre counter and closed games over open games. Also, what resources should I use on this website?
Thanks
The basics areas are openings, strategy, tactics, and endgames. I recommend reading at least 1 book on each plus a book of annotated games.
If 5 books seems overwhelming, you of course don't have to do that many, or if you do it can be spread out over many years. Just pick an area you're interested in (you mention strategy and openings in the OP) and go for that. As a new player anything you learn will help you improve.
As long as your openings aren't total trash, and as long as you're comfortable in the middlegames they produce, then you don't have to change openings... you can if you want, but often beginners try to solve other problems by switching openings all the time. Try to stick with the same openings for at least a year and actually learn them and get experience with them before switching. It's also good to pick classical openings (1.e4 or 1.d4 and follow opening principals) but some people don't like that, so again it just depends on how much fun you want to have vs how much you want to improve. (If you're lucky, the things that help you improve are fun!)
Ideally you play OTB tournament games where the time control is at least 60 minutes... but just like with the book thing if that's unappealing just play whatever you like. You'll still improve even playing blitz and reading books, just not as quickly.
This site has instructional videos, an opening explorer, tactics trainer, and other things. You'll need to be a paying member though.
Possibly of interest:
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/
Winning Chess by Irving Chernev and Fred Reinfeld (1949)
https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf
Back to Basics: Tactics by Dan Heisman (2007)
https://web.archive.org/web/20140708233537/http://www.chesscafe.com/text/review585.pdf
https://www.chess.com/article/view/book-review-back-to-basics-tactics
Discovering Chess Openings by GM John Emms (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf
Chess Endgames for Kids by Karsten Müller (2015)
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf
Seirawan stuff:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
https://web.archive.org/web/20140708092617/http://www.chesscafe.com/text/review560.pdf
https://www.chess.com/article/view/book-review-winning-chess-endings
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
http://www.nystar.com/tamarkin/review1.htm