I am able to develop my pieces systematically and purposefully. I am also good at defending my pieces. However, when the game gets closer to an end, I need to be able to see different mate variations easily. But alas I am having difficulty seeing them. As a result, I often start losing my positional advantage and win the game in more moves than it should actually take. Thanks in advance for your help!
The situation you find yourself in, is actually very common and also an issue for most amateurs. I think you will find out soon that there's no "one" answer that works for everyone. But there are of course suggestions that you may find useful:
Most promising way to improve your ability in finishing up games or checkmating, is solving puzzles. There are so many good puzzle books, websites/apps... you name it! Just start practicing and try to solve them, and in no time you will notice your improvement. Why it helps you may ask? think of it this way: Knowing how to finish games (or finding checkmates) means being familiar to the patterns present in your position (each game has its own details), and a pattern needs first to be noticed. To notice pattern/combinations/ideas, you first need to have been exposed to them in some way. That's what chess puzzles mainly do for you: they expose you to all sorts of ideas and force you to find them as otherwise you cannot solve the puzzle. Whereas just playing games over and over does not do the same for you, because there, you're not limited to one solution and instead of trying to find the right patterns(shortest finishes/checkmate paths) you just go with your already-made-intuition.
Second best suggestion I can think of, is reviewing your own games with an engine. Engines are in my opinion very much mis-used these days. They are amazingly productive when used to assist you while reviewing your already-played-games. With an engine, you will simply see where you may have missed out on some of the shorter paths towards finishing the game etc. Specially endgames where you have huge advantages, and you still find yourself playing out 20 moves, with an engine you will be fed the right ideas right off, so try to mull over them and don't just take them lightly. By doing this for most of the games you play, you will gather a very important amount of tactics/ or just useful ideas, that will help more easily concretize your advantages towards victories!
Some known and nice chess websites:
- Tactics and puzzles in chess dot com are great too.
- Finally whatever phone you use, I'm sure you will find many free apps for chess puzzles.
Recommended chess books containing puzzles:
- The Ultimate Chess Puzzle Book, very famous, written by John Emms
- Another great one is, Garry Kasparov's Chess Puzzle Book, but of course it's not best if you just want checkmate puzzles.
- A favorite of mine is, John Nunn's Chess Puzzle Book, which again is not only about checkmates, but instead contains all sorts of very advanced puzzles.
- Of course the list can be very long, but do bear in mind that when it comes to checkmate puzzles, you don't really need to find the famous books, you just need any decent collection of them, (in any library you will find many relatively unknown puzzle books, that will perfectly do the job), as the idea here is to "gather as many ideas as possible" so in your own games you will notice and re-use the learnt patterns.
In order to conclude, the more puzzles you try to solve, the more games you study, the more you simply watch chess games, the richer your bag of ideas/patterns/combinations will become.
I'll try my best to answer this rather ambiguous question however I'd like to note that if you want help in chess your best bet is to familiarize yourself with terms like "tactics", "strategy" and so forth.
A little bit on 3 major terms in chess, or at least how I perceive them to be:
patterns in chess(calculable) that lead to something factual such as winning a pawn, winning a piece, mating and so forth. Usually a forced sequence of moves.
Really just the general plan you're following. If you try to pressure a certain square or use a sequence of moves to go on the offense and had that as your plan that's an implementation of a strategy.
- Positional play
The most ambiguous term, it's generally just logical chess; Knights are strong in the center so you'd play your knight there if you had the opportunity. You don't follow a particular strategy nor did you calculate variations to see if this knight will lead to a definite advantage but because experience and general chess knowledge dictates knights are strong in the center you can conclude there is no downside to having it there, the opposite even.
All these terms can become moot easily, miscalculations, positional play that's not backed up by proper think-work and strategies that become invalid due to the opponent playing out his own game... You get the point.
So what we're looking for here is the term tactics, the pure act of seeing forceful moves that lead to a certain advantage. Tactics are something usually gained through practice and lots of experience, it also helps when you are familiar with the basic mates(mentioned before like King+Queen, King+rook, and King+2xbishop or King+bishop+Knight if you're feeling really up to the task) but also mates that simply involve certain patterns. Here's a supersimple one but you get the idea:
1K6/PPP5/8/8/8/4r3/3k4/8 b - - 0 1
There's a few ways to practice tactics:
Books that involve endgames will always be great, they involve a great deal of tactics and will surely strengthen your ability to see them throughout the entire game.
Chess puzzle books are another great idea.
Let's not forget this great resource called the internet, there's websites out there with tactics trainers designed to take in account your playing strength as you do their puzzles. Two of these I'm aware of are:
Especially Chesstempo is a great resource.
Solving tactics puzzles that end in mate should help a lot. Even if the puzzles are short (2-3 moves), you will learn all kinds of mate positions which is useful because you will know what to aim for in longer mate sequences.
In practical play, looking for long mate sequences is not necessarily the best choice, particularly if you don't trust your calculation skills. Often this happens when the mate requires you to make quiet (not forcing) moves or if you are under time pressure.
In some cases you might rather want to play a simple forced line that simplifies the position and leads to a clearly won endgame for instance.
I have found that the "Practice" section of Lichess.org has great examples, specifically because they guide you through standard Checkmating patterns (e.g. Boden's Mate, Arabian Mate, etc.) They also tell you how many moves you should make for each of the problems (e.g. Checkmate in 3 if played perfectly), which I have found to be quite helpful. The site also has other helpful practice problems (tactics and pawn endgames), I highly suggest you check it out!