Can't really study for the skills test. I can tell you the 2 main areas people always fail is the walk around inspection and the brake check portion if doing air brakes. You must get all 3 parts in the correct order or else it's immediate fail. Bwing able to back is a definite must, you might even have to parallel park. I had to parallel park a 30 foot wrecker that was towing a 35 foot transit vehicle, but my boss, who took the test the same day I did (different examine administered his), did not have to parallel park. It all depends on the examiner.
For the written test, go to Trucker Country | Helping Truckers Since 2004!
They have tons of practice test for you to take. I believe they have everything but school bus practice test now. They are a wonderful source for the general knowledge, air brakes, and passenger test (and anything involving trucking). When I took the 5 test I had to take, every single question that was on my exams, they had in their practice test.
If you can pass their practice test, you can pass the computer/written test just fine.