3. Eating the right things at the right time
At most, CrossFit competitions you will have 3 to 4 workouts a day. If you are attending a multi day event, it may add up to 8 workouts in two days, which is extremely demanding for your body and its functions. In most cases the only normal meal will be the breakfast. Focus on that! This could make the difference during those days competing.
Try to consume up to 1000 calories (I am not kidding) at breakfast. It will build enough foundation to offset at least the first workout. Eat breakfast 2-3 hours before the first workout. Later, eat and drink after each workout, even if the WOD was one max rep lift only. There are thousands of CrossFit competition articles on what should be included in those meals. In reality athletes will even find it hard to eat anything. Therefore just eat something.
I tell my athletes to make an eating plan beforehand and stick to it.
4. Warm up for every workout
This seems to be a no brainer, but in reality every competitor is warming up for event one only. I barley see any CrossFit athletes in the warm up area after events 2 and 3.
Warm up should stay in the sub 20 minutes time frame. There is no need to warm up for a whole hour, especially when four events are coming that same day. I personally have a 3-time 5 minutes rule. Five mins of a general warm up (row/run), 5 minutes of specific (movement prep for the particular CrossFit workout) and 5 minutes WOD flow prep where I test upcoming movements.