After my game last week,  I, being upset by the blunder, started to analyze my games.
I got even more upset after that.  I found, that in the 1st tournament in the new club
I made a mistake, allowing simple tactics 1,  lets say 1.5  times (second wasn’t very simple) in 5 games,  my performance rating was ~2100. In the 2nd tournament same in 3 out of 6 games, PR = ~1900. In this tournament 2 out of 2, PR = ~1700.
I made a little research and found some interesting stuff from Dan Heisman.
He says that 1200 rated guy makes 4 mistakes (allowing simple tactics) per game, 1600 – 1 , 2000 – 1 in 4 games, 2400 – 1 in 16. It correlates very well with my stats. He offers some advice with regards to this. First, when you choose finally the move out of a few candidates, don’t make it right away. Spend at least 15% of the time, that you spent before on all candidates, just checking this move: checks, captures, threats. Also, he says, a lot of tactics that people solve easily doing exercises, they do not see right away at the board. He says, I see much more patterns than my students without checking and calculating, like we see back rank mate.  I looked again at my last games and I found:
fork, trapped piece, removing of guard, pin, discovered attack, double attack – 2 of each.
So, using the first letters, I got – FTRaPeDD or f&#@ing trapped! 🙂
I decided during my next game to repeat that last sentence before each move.
Yesterday  I  got a pairing with the boy,  judging by his look, first moves, etc. rated ~1600.  It wasn’t far, after the game I found he was rated ~1550.
I was White, Ruy Lopez, Chigorin variation, here is the game. The guy played fast the first 10 moves, then played unusual to me 11. … Nd7.  Though I didn’t quite like it,  it’s actually a second line, Keres played it a few times. Anyway, his 14th move was out of book and on 15th he made a mistake.  I said my motto and saw that he loses a pawn. I got an attack on the kingside and on move 26 he made a decisive mistake.
On move 29 I missed a possibility of mate in 3 – Qg3!, it was a mating pattern with bishop on a1-h8 diagonal and knight, mating on h6. Anyway, after 11 moves the mate was inevitable and the guy resigned.