Most feasible ideas have probably been presented already. Here's my personal list.
1. Tactics. Spend most of your time on tactics until you are sick of them and instead want to play actual games. If you don't know the tactical themes out there yet, I personally recommend the "Step Method" by IM Cor van Wijgerden, but any resource will do - I've seen some very good YouTube videos about beginner tactics that serve as a good start.
2. Play and analyze games. Play the game according to Betelgeuze's formula, keep time control in mind as tpr pointed out, and analyze the game afterward with the help of an engine. Of course, the engine is a TOOL, not an excuse to stop thinking and start letting the engine play vs. itself.
Playing games slightly strengthens all aspects of your play, although at a slower rate than if you practiced them separately. Benefits are that you learn certain things that only pertain to classic chess and NOT to the practice of its individual elements (such as common tactics and ideas in the openings you play). It's also fun and helps you evaluate your play and thus allows you to identify your strengths and weaknesses. Strengths are something you can use in deciding what openings to play and weaknesses are something you can use in deciding what to focus your practice on (I can already tell you the answer, though: TACTICS! :^P).
3 - 99. Tactics
100. Endgame studies once you're in ethereally high Elo planes.
101 - 999. Tactics
1000. Discussing with your team what move to play after 22. Bh6 in some main line Sicilian. (This is a pun that partially revolves around this point being so far down the list it should be the least of your concerns.)
I personally don't like any form of writing as a means of studying chess rather than merely discussing it. I'm sure they also serve as a good way to improve your game, but I personally am convinced that the formula puzzles + games + analysis is sufficient. I haven't ever read anything in a chess article or book yet that I have considered to be clearly useful in my games, while in complete contrast it's hard for me to think of a puzzle, game or analysis that did NOT help me improve. But, of course, many have used it to improve and it's certainly not a bad way to practice. I just didn't put it on my list because I think it's unnecessary and there are better ways to spend your chess studying time.
Also, you cannot evaluate whether or not you stagnate if you don't play regularly. Go ahead and look at my Elo curve; it's ever so slightly climbing. However, that's not based on 10 or 20 games. That's based on hundreds of games with hundreds of puzzles and analyses in between. Remember, rating gains are something LONG TERM. Losing even as much as 50 rating points is no big deal; what matters is that you're improving and that eventually, you'll get those points back with some nice tax rate on it as well. Consider that Magnus Carlsen played 3000 games when he was 12 years old in ONE YEAR. Then you realize that before ever questioning your capabilities or "talent", you should first question how much time you're putting into the game. And I can tell you right now: if you are not a GM and are capable of reading and comprehending this text, you far exceed the minimum cognitive requirements to play chess at a solid level. Drill that into your brain! YOU DO NOT LACK BRAIN POWER IF YOU CAN READ THIS!
One last thing, about early resignation. Early resignation and questioning your capabilities are a sign of low self-confidence. Obviously I hope they are retained to just the game of chess. Either way, it's a serious issue and it's something worth workin on just as much as studying the game itself is worth. I just looked into one random game and you resigned with only a pawn deficit resulting from some complicated positional weaknesses at best play. In other words: it was completely even for practical purposes. You probably resigned because you thought you dropped your queen, but you were attacking the opponent's at this time. Point being, don't resign until you have so little pieces left on the board that it's impossible to get a sufficient amount of material back. At my level (1700-1800), I bet I win roughly 1/3 of the games after being down a full piece. I've even won a game once against someone with a similar rating down a Queen, Rook, Bishop and Knight. OK, that's a once in a lifetime, but at your level you only need two pieces to go ahead and threaten checkmate. Oops, opponent missed it, you win.
So now that the part about the utility of not resigning early is out of the way, I want to discuss the mindset that underpins it and some advice on how to get rid of it. Much like you need to exercise the same tactical concepts over and over again to really drill them into your brain, the same applies for your mindset. This is something many different people have picked up on, including sportsmen, soldiers, and cognitive psychologists. To take that game I saw as an example (
lichess.org/xVZbUgny): I assume you resigned because you noticed you'd lose your queen. We'll ignore for a second that you actually would trade queens instead. In this situation, you should always establish your winning condition and focus on that. Down a rook? Attack one of his rooks. Opponent too clever for that? Set up a double attack onto his rooks. If you still have that queen, go ahead and launch a kingside attack; checkmate is always a winning condition, but it's most feasible with queens on the board. Opponent down on time? Run him out of it. Generate counterplay with the above options in mind and do so quickly. Have him budge under pressure. DO NOT do this when ahead; in that case, playing slowly and calculated is the way to go. Why? Because of your winning conditions! If you're ahead, staying safe and playing it out calmly is a win for you. We're only looking for cheap tricks because it's our only potential way out, of course. This is how I think during a game. I try to resign only when I see no more feasible win condition like checkmate, win on time or playing for tricks. But until that very moment that I hit the resign button, I am thinking "I CAN WIN!" without any hesitation.
Besides this, you have to accept that if your opponent does not fall for your tricks, you lose the game. After I see I missed a double attack, the first thing I do is accept it. Don't take three minutes in a four-minute game to desperately look for a way out when you really know it's not there. Look for your most realistic win condition and say "I will lose if my opponent plays correctly, but I COULD WIN! And my win will most likely come from <win condition>". Notice that this is a slightly adapted model of the "5 stages". First, you're angry. As long as it's not too intense and subsides quickly, then this is fine. Then you accept that you made a mistake and are most likely going to lose. Then you "negotiate" or see what your best odds of saving the game are. It's normal to spend a bit of time to spot for a resolution to the tactic played against you before accepting it, but some players head into denial and spend ludicrous amounts of time after they notice they are now officially losing. That's a whopping 4 out of 5 stages, skip denial if possible, maybe even skip anger if possible, although some level of frustration is normal. Chess is life, losing is dying, I guess. Then what would winning be, though?! But yeah, in all seriousness, train yourself in this area. Especially because most likely if you have this issue in chess, you'll have it in other games or areas of life as well. And it's something you can actively do something about through cognitive exercises like this!
Good luck!
