So I just got this the other day.
I was having trouble with finding anyone in some of the foreign language rooms, and the ones I did, the people playing were actually very good and usually i would only make it above 30% of the people.
I tried something different, I used an online boggle solver. (I know, cheating right?)
I used this one: http://fuzzylogicinc.net/boggle/
Choose 5 letter words to narrow it down to the higher scoring ones.
As soon as the round begins, quickly enter the puzzle and click "solve puzzle"
(when you have a split letter (eg. M/U) pick one of the letters)
Some of the words are not correct in the game, but most are.
You still need to be fast, but at least you can grab the high scoring ones. After you get yourself a bunch of points, if you have about 30 secs left, just do the easy 3 letter words to bridge the gap.
To get above 50%, you'll need a score of above 400 points, likely closer to 600.
Best of luck.