just like anything else in the game, really. First, time controls matter... if its a game in just a few min/side or even faster, there is no way to spot every missed opportunity. If it is days for each move, there is no excuse (and I am as guilty as anyone of not using my full time to look, but there still is no excuse).
As far as recognizing them, look at the opposing king. Test 1 ... can it move at all? If it cannot move, it is called a "stalemated king" and is vulnerable to mate IF you can check it. Examples include a king surrounded by its own army killed by a knight, or a king that can't move into various checks awaiting the final ending move. Test 2... can it only move to a very few escape squares... back rank mates, for example... the king can only move along the back rank, trapped behind its own pawns, a rook or queen back there and its over. The third test is the "well developed king' ... a king that has been forced up into the middle of the board can often be trapped and mated there.
In any case, its just recognizing the opposing king's vulnerability and trapping it. Sometimes it is already trapped by its own pieces, and other times it is exposed so it can be "walled in" by rooks or queen. If you have the time in the game, stop and look hard at the king -- how can you trap it?
The one in this game is tricky enough to spot in a hurry.
Missing mate in one seems to be my favourite type of blunder in recent days. But this example was particularly spectacular. The game itself was certainly nothing to write home about, but after 22...Ne4 I threatened 2 possible knight forks. My opponent avoided one, but only by turning the same N move (23...Ng3) into an immediate and beautiful double-knight mate instead! But ... I missed it, rushing instead to take advantage of the other fork. C'est la vie.
But, having missed mate-in-one opportunities 3 times in the past week, I'm hoping for some advice on how to prevent it happening again.