Opening instructions for below 1000

I have an idea of how beginners could learn and should study openings. What I am doing right now is that I go trough the games aftetwards (as always) but pay attention to when I went from book moves or green moves to mistake or bad accuracy. Then I try to remember the move suggested by the computer as the best. This usuallt happens around move 3-4 or so. I hope this is a good idea. I do not have the memory or knowledge to memorise deeper lines (and I know beginners should not do that) but I hope this could be a way to not mess up in the first moves. Most of my opponents are under 1000 so after like move 5 we make random moves regardless or moves where chess understanding (not opening theoey) is enough.

"... Create a simple opening repertoire (understanding the moves are far more important than memorizing them). ..." - IM Jeremy Silman (December 27, 2018)
https://www.chess.com/article/view/little-things-that-help-your-game

Perhaps it would be a good idea to start with Discovering Chess Openings, a book about opening principles.

"... For beginning players, this book will offer an opportunity to start out on the right foot and really get a feel for what is happening on the board. ..." - FM Carsten Hansen (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

"... Review each of your games, identifying opening (and other) mistakes with the goal of not repeatedly making the same mistake. ... It is especially critical not to continually fall into opening traps – or even lines that result in difficult positions ..." - NM Dan Heisman (2007)
https://web.archive.org/web/20140627062646/http://www.chesscafe.com/text/heisman81.pdf