I would suggest if you can't answer a question within a few seconds, move onto the next.
If you finish with time to spare, go back and see if you can come up with something for those questions. If you are really stuck and are learning to one answer, put it down. Better to guess and have a 1 in 5 chance of getting it right then a 0 in 5 chance.
I'm pretty sure the answer to the second last question is actually B, not D.
Remember, that even though there a four separate papers, they all have the same letter answer. Means you only need one marking grid and, in these days of cutbacks, that means savings in the region of Â£2-3 NATIONWIDE!
If you're slow at times tables, write them down during the practice exercise.
Work out degrees on a clock, eg. 15 mins is obviously 90, 30 = 180, etc, but work out 1 minute and 5 minutes too. There may be a series of questions about it and it saves you working it out on the day, when you only really have time to do the adding up.
Like others have said on here, it cannot be reiterated enough how crucial timing is.