What are the most important and useful strategies you have learned as a beginner?

A High-Value Tactical Manual for Chess Beginners

I haven't been playing chess for a while now, have been busy studying certificate 3 and 4 in fitness. I should graduate in a few months time hopefully, and want to get back into chess

From what I remember from playing more actively a few years ago, the main advice I was given is to not make moves too quickly, as that can lead to massive blunders and leaving pieces hanging or undefended. So many games I am winning comfortably until I get reckless and move too fast and end up losing important pieces.

I really like the advice given here 
The Three Universal Tactics Every Beginner Must Master
The Fork: A single piece attacks two or more enemy pieces simultaneously. Knights are the ultimate asymmetric weapon for forks, but pawns and Queens can execute them with devastating efficiency.
The Pin: An attack on a piece that cannot move without exposing a more valuable piece behind it (usually the King or Queen). A pinned piece is functionally paralyzed, losing its absolute strength.
The Skewer: The reverse of a pin. An attack forces a highly valuable piece (like the King) to move, exposing a lesser-valued asset behind it to be captured.
The Analytical Habit: Before making any move, perform a Two-Step Blunder Check. Ask yourself: What is my opponent threatening with their last move? and If I move this piece, what square or asset am I leaving unprotected.

What are some of your favorite beginner tips