From 1400 to 1500 : Study the chess games of Paul Morphy
One thing that most 1400 players  can learn is that piece development and king safety are sometimes worth much more than material win in chess.
And the more experienced a beginner chess player gets, the more likely the material win will be more often replaced by fast piece development and sacrifices for checkmate or for a bigger goal than winning one unimportant looking pawn.
What I would like to advise beginning chess players who tend to want to grab unimportant pawns (or defend unimportant pawns), and neglect piece development related to that, is : study the chess games of Paul Morphy.
The chess games of Paul Morphy have been important for the chess of Bobby Fischer, and have partially defined his playing style.
Paul Morphy has played several amazing chess games where piece development was important, and often companioned by sacrificing one piece after the other for the highest goal in chess : checkmate !
Let's have a look at the famous Opera game :
Another reason that beginning chess players should study Morphy's (annotated) games, is to avoid making the same mistakes as the opponents of Morphy !
See here a game I just played :
See also this article by GM Serper :
 Note : I'm using 1400 rating here, just for practical reasons. It could be 1200 or 1300, and I realize that a fairy good and experienced chess player can still be stuck into 1300 or 1400 for various reasons. For example concentration problems because of personal life issues, or being sensitive for noise, or decreasing memory issues, or confusing various opening lines, not learning from mistakes etcetera.