How do I improve my checkmate skills? 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!
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:


Tactics


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.


Strategies


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


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.


Websites


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:

www.Chess.com
www.Chesstempo.com

Especially Chesstempo is a great resource.