Actually, even though I'm teasing Pappers (a lot) about this- he was extremely helpful to me in getting ready for the test.
I don't have a homebrew club and I live in the middle of nowhere, so I was prepping totally on my own. Pappers' advice helped me quite a bit with getting ready for the tasting portion. He tested about 6 weeks before me, but we got our results on the same day so our exams were scored at the same time.
His advice is helpful and I really appreciated it. It's probably more helpful to take a class or two through your homebrew club than attempting what I did and doing it alone- but my certificate is proof that you can do it on your own as well.
The tasting exam isn't hard at all- IF you know your beerstyles. In a real competition, it's much easier as you can have a copy of the guidelines in front of you as you score. During the test, you really have to exhibit that you know the guidelines for each style. You can't really say "too much" at all- but you can say too little.
A rule of thumb that Al Boyce told me is to give one piece of corrective advice for every 10 points under the score you give. That means, say, for a 30 point beer, you give two very good points of advice. Not "watch sanitation", which is easy to say. But to say, "The staleness could be signs of oxidation- make sure that transfers are done without splashing to avoid oxygenation" if you gig the beer for oxidation. If the beer is infected, talk about sanitation and how to avoid infection, not just "watch sanitation".
And if you've got a seat in a tasting exam- good for you! I know Pappers (who lives in a HUGE metro area) had to travel for his exam, and I traveled to Minneapolis for mine.