The most test is a funny test... It has been almost 2 years since I did it.
It is a pattern recognition, mental math and learning speed test. You could do some IQ Tests as a warm up and then do some mental math review. Go over things like multiplication in your head and divide big numbers by other numbers, like how many times does 17 go into 374? It is a timed test so you have to be quick about it.
All I remember is that all the candidates for MARS at my NAOB did it first, and they had a wide range of university degrees but not too many math intensive ones and not all recent grads. A lot of them came out complaining how tough it was and how they ran out of time. Then the next day the engineers took the test and most of us were fresh out of university and we zipped through it with no problems, waiting around for each timed period to end so we can go onto the next phase. The difference in outlooks was quiet humorous.
If you want to be a MARS officer, practice mental math, simple things like 3,6,8,9, and 16 times tables, fractions of 60 and math like (5x6)/3 which tells you that your CPA to buoy that is 5 degrees off your starboard bow at 6 miles is 1000 yards, which can alternately be worked out by knowing that 5 is a twelfth of 60 and a twelfth of 6 miles is 1000 yards.
Don't worry about the MOST too much. It isn't that hard, it is just a little fast.