From my experience, the key to doing well is not to get good at writing more or writing faster but rather to increase the information density of your writing. The rules allow for abbreviations which should dramatically speed up the writing process. My partner and I also spent a few hours discussing how we would describe some common objects such as Legos and office supplies so that when they showed up at competition, we were already viewing the instructions from the same reference point. In addition, agreeing on the meaning of direction words such as top/bottom, north/south, 1o'clock, front/back, etc. beforehand will go a long way. For common construction kits like K'nex and Legos, it's worthwhile to just come up with a standard notation.How do you get good at writing quickly?
But with regards to your question, you could also try removing any superfluous words used in ordinary grammar like articles and some verbs if you're really looking to write as fast as possible.