Do not telegraph
When fighters stand relatively still in the ring before they attack, they telegraph the attack. When fighters, without changing the rhythm or tempo of their movement, initiate their attack on cue with the beat they have established, they do not telegraph the attack. Attacks should be similar to way a fencer quickly and non-telegraphically closes the distance on the opponent. The attack should take the shortest route to the target without any preparatory or telegraphic, set-up movements. As Bruce Lee said, "Use the longest weapon to the nearest target!"
Do not concentrate on techniques or combinations
If you are thinking about a technique or combination to use, it may be wrong one to use by the time you use it. Instead, concentrate on reading the opponent, watching for openings, and creating openings. When an opening appears, fire your nearest weapon into the opening and follow up with combinations that are appropriate against the opponent's blocks. Trying random techniques and combinations are a waste of time and energy unless there is an opening for them to score.
Do not think. During the fight, do not try to analyze your performance. Analyze your performance during the breaks between rounds (with your coach if permitted) and then put it into practice.