How to spot double attacks?

Im analysing matches after i played and im noticing that i miss alot of knight/queen double attacks, does anyone have tips on that? Im rated 680 on rapid. (Like the picture below)

Go to puzzles and there is a misnamed puzzle game called solo chess.  The object is to leave just one piece on the board.

Drill puzzles that contain the pattern. Many books and websites group puzzles by pattern so you can focus on a weakness. Little and often is better than irregular binges. There are also methods such as Woodpecker and Spaced Repetition. Give it time, weeks/months and your ability to quickly spot these will strengthen as the brain automates it.

I feel that this is an area that deserves more attention in general. When people are talking about tactics, they always say 'just do a ton of them'. That is true, because it teaches pattern recognition. The idea of that is that you'll spot the tactic in your own games, because you've solved so many of them that the pattern will stand out to you when you see it in another position. 

However, that advice is not complete and this post shows exactly what is missing. The question is not 'how do I get good at tactics', the question is 'how can I spot them?'

There are techniques that will help you spot tactics. For this you need to better understand how tactics operate. Let's take the double attack as an example. A double attack works when you attack 2 things at the same time. There are essentially 3 threats you can make: 
- a threat to the king (check)
- a checkmating threat
- a capturing threat to your opponent's piece

Now check and threatening checkmate are the most forcing threats. A threat to capture an opponent's piece can be a threat or not at all. If my queen attacks your knight, but that knight is simply defended, then it's not a threat. If my knight attacks your queen it's a threat even if your queen is guarded, cause the queen is more valuable than my knight. 

Threatening to capture a piece is a threat when: 
- the piece is unguarded
- the piece is worth more than the piece attacking it
- the piece is insufficiently guarded. For example: my knight attacks your bishop, which is guarded only by your rook. If I take your bishop, you'll simply take back with your rook. But if I bring more threats against your piece, say my queen attacks the piece too, then you won't be able to take back my knight with your rook, as my queen would then be able to take your rook. 

To spot tactics you can therefore use the following technique. You can use this every time you play a move, with puzzles, basically any time. Look for all the moves that put your opponent in check, look for all the moves that threaten checkmate and look for all the moves that attack unguarded pieces, insufficiently guarded pieces or pieces of a higher value. If you notice that a certain move threatens more than 1 thing, you'll have spot the tactic. 

So, to put this technique to the test in the position above. Say the white knight would be on e5. 

Checks: Nd3+, Nf3+ and Qh4+
Checkmates: none
Unguarded pieces: none
Insufficiently guarded pieces: Qd2 (attacked once, defended once). How can I attack it? Nc4 and Nf3. 

Hey, Nf3 was also check, so that must be a double attack!

Hope you'll find this helpful. 

But wait: you learn to spot them by getting relevant puzzles wrong and looking at the solution.  “Do a ton of them” answers the question.

Working backwards can help too.   How can you double attack?  Every piece can double attack, but each one does it differently -- take a short look at them:

A pawn can double attack with a pawn fork.  Basically, moving a pawn forward will attack 2 pieces at once on the two diagonal squares that it attacks.   This is an extremely easy one to spot: pawns can only move forward 1 or 2 first time squares, and they can only attack 2 squares ever, so a little study on this one should have you good to go on spotting it both defensively and offensively.   Even higher intermediate players miss this one at times, though, esp in high speed. 

the knight is next.  A knight attacks in a circle around it, really.  It is well known to be able to attack 2, 3, or even more pieces at once from a single square.  Beginners struggle to spot these because the knight 'moves strangely' to beginners and it takes a while to get a feel for it.  There are plenty of in depth studies on the knight. 

the bishop is like the pawn, but on steroids.  It can attack 2 things at once along 2 diagonals from where it is places.  The most common of these include hitting the king and a rook at once, scoring the rook, but there are many times when it can tag both rooks at once, and other targets with the same idea can land anywhere on the board.  It can also, more rare on the board, hit the same diagonal on both sides to double attack: this is the same idea that just happens to share the diagonal instead of being more V shaped. 

A rook double attacks by an L shape or a straight line.  If it can move between two pieces on the same rank or file, it can do it, or if it can hit one on a rank and the other on a file.  

The queen combines the rook and bishop (which incorporated the pawn idea too remember), and adds the idea that it can hit the diagonal AND a rank or file attack at the same time as well.   If you have practiced the rook and bishop ones, adding this single new idea will wrap up the things to look for and practice. 

if you have a real chess board, maybe drop 4 or 5 pieces of one color at random on the board and then pick up a piece for the other color and try to attack as many of the pieces as you can from any square.  Try that for a little while, then start doing the puzzles or trainers with these ideas. 

PS: don't forget the king.  It can basically double attack and more any number of pieces that it can reach in 1 move.  Any pieces that share a single square that the king can reach is at risk of it, though such aggressive king moves are rare indeed, its uncommon to be able to attack more than 2 at once with a king AND ALSO be willing to jump out in the battle like that with the piece.  Its the kind of thing that happens if the king's owner is already desperate and spots an opportunity that outweighs any risks, or its deep endgame and the king has grown into a fighting piece.