Here are two relatively simple endgame-related principles from which a typical Elo 1300-strong player could profit.
PAWNS ON SQUARES BISHOPS CANNOT REACH
When some but not all bishops have been captured, the 1300-strong player can learn to push his or her pawns to squares of the color the bishops cannot reach.
Here is an example from an actual game. The Black player's Elo strength is about 1300.
[FEN "8/pb3kp1/2p1p2p/2P1Kp1P/1P2pP2/P3P1P1/2B5/8 b - - 2 33"]
[Title "Black to move, the board seen from Black's perspective."]
In this game, White had been playing tactically until Black unwisely let the dark-squared bishops be exchanged. Foreseeing a won endgame, White stopped playing tactically, quickly exchanged rooks and queens along the open d-file, and soon reached the diagrammed position.
Material is equal, but White's bishop
- enjoys freedom of movement and
- sees enemy pawns on squares it can target.
Black probably never realized that his game was already lost. Indeed, Black probably left the board without understanding what had just happened to him, because he did not grasp the principle of pawns on squares bishops cannot reach. White won a game Black should probably have drawn. Black never knew why.
Now you know why. Next time in such a situation, you can do better.
If your strength is about Elo 1300, then you might add an easy 20 to 25 points to your strength merely by recongnizing—before the endgame arrives—how the colors of the squares on which the pawns stand can advantage the one player or the other once the endgame arrives.
KINGS BEFORE PAWNS
Players at an Elo strength of 1200 often fail to hurry their kings toward the fifth or, better, sixth rank when the endgame arrives. Some 1300-strong players too fail in this way. In the example, Black might have salvaged a draw if his king were further forward.
This is actually a complicated point, because sometimes it is preferable to push a pawn toward the seventh rank as soon as possible, temporarily leaving the king far behind. Admittedly, better players (Elo 1800+) disagree among themselves as to the general desirability of such pawn sprints, but even when a sprint is tried and even at the Elo-1300 level, the sprinting pawn tends to distract the opponent long enough for the king to be brought up a little later, so the principle still applies.
Most good players agree in any case that leaving pawns at home while the king hurries forward is often a prudent endgame practice, especially if all relevant pawns are on the same wing but sometimes even when pawns on both wings are in play. Once the king has centralized itself, preferably at least on the fifth rank, pawns can march as opportunity allows.
Kings before pawns: a little reflection on this principle can add another 5 or 10 points to one's strength in the 1200-to-1300 range.
Computers can calculate or tabulate absurd numbers of exact endgame variations a human master would never attempt. Therefore, it can be hard to learn proper endgame play when one's opponent is a computer. Playing Black, a computer might salvage a draw or even a victory in the diagrammed position, not only taking the game but also cheating White of the position's teaching value. For this reason, a 1300-strong player might prefer human opposition against which to practice endgame principles like the principles this answer discusses.