Hi Debs,
Skytest is the best investment you can make. Of course with dedication and lots of practise, no reason you should fail. For ab-initio guys, physics might be a bit of an issue because it's more about good understanding of the principles but you won't find it in skytest. You really need to revise your high school physic books if you are not already familiar with it.
Having said practise would do anything better, visual memory part is really something beyond skytest or anything else you find in the market. I cannot advise enough to do more work on this than any other part of the test. I haven't managed to find out what exactly improves visual memory myself but it was really hard to focus and try to memorize all the symbols in a short time and remember the first symbol you saw....
Best wishes,
LB