1 huge thing on essays is to spend sufficient time outlining. This is how I set up my outline:
Outline (gets 5 min minimum and 10 max)
Intro
define the terminology in the prompt in a manner in which it applies to my own argument, introduce general themes and examples I wish to discuss, end with a strong thesis
Points to support thesis
Points to refute thesis
conclusion
repeat thesis, link the support to refute examples in a smooth, logical transition. look at overall picture and universal implications and why we should really care about the prompt.
Don't get too flowery in linguistics, you want to be clear for your reader (who has read too many essays to keep an appropriate focus). You want the essay to flow logically and the only way to do that is to have an effective outline and appropriate opening/closing statements within each paragraph.
I was in MUN back in the day and took a lot of poli sci/classics classes so I am pretty well versed in different topics. But if you focus on a few topics of interest you should be in good hands. I would know Thucydides, Machiavelli's Prince, Ghandi, FDR, MLK...know what the UN does and its history. Knowing something about these topics will clear out 80% of the "data base" you need to access for the sample.
I scored a T on my second MCAT, and S on first. I am a bio major not a poli sci, humanities or communication-heavy major.