He begins by acknowledging that there are several emotional factors you have to face, some for you and some against you and the trick is to accentuate those in your favor and diminish the negative factors. It takes a conscious effort to adjust your thinking pattern to the game situation because if you can't, then your play is probably going to be based on emotional factors.
Frequently the worst, and one of the most common, mistakes to make is to deviate from opening setups you are familiar with. Usually this is because we think our usual openings are not good enough and our opponent may have a better understanding of them than we do. In those situations it is a frequent occurrence that a dubious opening will be chosen, studied briefly and then in the game we play the first 10-12 moves correctly before getting disoriented and don't have the slightest idea how to continue. Yermolinsky wrote that there is nothing he wanted than to have his opponent avoid theoretical lines trying to surprise him. The reason is that a dubious opening will give him a good position with plenty of pieces on the board and he will find a way to outplay anybody 300 rating points below him.
The best thing to do is play the sharpest lines in the best openings. You'll probably get outplayed in a long game, but if you can whip up an an attack from a sound position, you might be successful.
Most players buy a book or CD on an opening that has a catchy title like Play This Crap and Win! that promises success when they play it and then memorize the variations. What usually happens is the opponent doesn't play a book line or the player forgets his analysis or gets things mixed up. The result is mistakes are made due to a lack of understanding of the position.
I ran into classic example of this in a tournament once against an opponent rated a couple of hundred points below me. He was racing through the opening while I was playing rather slowly...a sure sign he was booked up. Late in the opening he sunk into a long think...meaning my last move was not in his book or he had forgotten the analysis. After his long think he made a huge blunder and lost quickly.
In the post mortem I got a lecture on the opening and when we got to the critical point he explained that my move wasn't any good. Why, I asked. The answer: Because it wasn't what Bobby Fischer played. Imagine that! My move wasn't as good as Fischer's. My only question was, "If it was so bad, why didn't you refute it?" All I got was a blank stare.
Another common error is trying to simplify at all costs in the belief that it will give better drawing chances. This is because of the belief that the higher rated opponent has superior tactical skills so we should avoid tactical situations. There's also the hope that the higher rated opponent, not wanting a draw, will reject good moves just because they lead to simplification. The truth is, nothing will make your higher rated opponent happier than seeing you trying to desperately simplify a position, because it often is done at the cost of positional considerations that will tell against you in the long run. Reducing the number of pieces on the board does not always simplify things.
Then there is a desire to create a material imbalance which usually means a sacrifice. This is often done because we think we have a better chance in an unclear position because the higher rated player is too good at positional play. Alternately, there is a fear of sacrificing anything because we believe our opponent is better at calculating.
Time management can also be a factor if we insist on checking and rechecking our calculations. This is often the case when we believe we are more prone to blunders than our opponent.
Inviting a crisis unnecessarily. We do this because we figure in long maneuvering games we will get outplayed. Yermolinsky also offered the advice that one should be careful before playing a freeing move because if they are truly freeing, the stronger opponent would likely have prevented it.
Playing defensively. We see threats, real or imagined, and figure it's better to be safe than sorry. The result is we abandon our plan in the hope of getting into a quiet position.
Attacking whether justified or not because of the fear that we may end up in an inferior position, especially if it means playing an ending.
Generally speaking, active play offers the best chance when facing a higher rated opponent.
Here is an example of of me trying to take my higher rated opponent out of the book and paying the price. When my opponent played the Bird Defense against my Ruy Lopez it didn't bother me because I play it myself sometimes. But, in this game I was outrated by a couple of hundred points and believed that if he played the Bird he was probably quite familiar with it. So my rationale for playing the unusual 5.Qf3 was 1) it deviated from a setup with which I, and probably my opponent, was familiar.
Then on move 12 I launched a premature attack before I had castled and finally 3) in an effort to simplify, at move 15 I made an unprovoked exchange which resulted in a near lost position.