I probably wouldn't do a prac exam (it takes too much concentration and if you can't do questions you'll probably panic), however, doing nothing would panic me even more. The number of marks I've scraped from that morning's study is phenomenal.
It really depends on
a) what type of subject it is (e.g. a content-heavy subject is easier to do this for than a maths subject)
b) how well you're prepared for the exam
These were the sort of steps I used:
1. Skim really quickly over the whole course (using the study design for guidance; 'Do I know X, do I know how to do Y...').
2. Note down anything I didn't know or wasn't that sure of.
3. From that, create a list of exactly what I wanted to cement, learn or practise, strictly ordered by importance (anything small or challenging I left till last as I probably wouldn't get the same return in marks from learning them as from learning something else).
4. Go through these one by one. Don't try to learn them all; just start at the top of the list and solidly learn/revise topics downwards. Remember that if you don't get far on the list, you've still learnt the most important things. Don't try to learn too many things, and keep going back to what you've just learnt/revised, because you can only fit so much into one brain in a few hours.
Other things I did included generally reviewing and reading my notes, and writing a list of 'watchouts' for the exam (specific things I wanted to remember all through the exam and not make mistakes on).
I found that 'doing' something calmed my nerves; also the last thing you want is to start jumping and flicking randomly through the course trying to cover everything all at once, because you suddenly start panicking because you can't cover everything and are going to fail. Keep it organised, and keep going over stuff again and again, and I personally believe you'll get a long way. But this is just my opinion.