For Samuel Merritt out in Oakland, the general theme of the question was how would you describe OT and how does it differ in philosophy from other medical professions. The handout that we were to write on had specific directions and I almost feel that half of our grade on it was did we follow the directions exactly. We were given 30 minutes and the room you were given to write your essay was enough for one longwinded paragraph, or maybe 2 short ones.
My advice would be:
Read your question carefully
Stay calm
Plan what points you want to make before you start writing
Address everything that is asked for in the question
Be concise, but if there is room, provide examples when you can
Save a line or 2 or 3 at the bottom to summarize your points
Spell check at the end (it's more important to make sure you finish your essay than it is to stop all the time to make sure you spelled everything correctly, ya know?)
Anyways, that is what worked for me. I did get in to my school, but I don't know how my essay ranked next to everyone elses.
Good luck and try and stay relaxed while you are there (very hard to do, I know...)