My advice: DO NOT STRESS! It's seriously a piece of cake! I took the HESI once in December, and I got much higher than I planned to. To prepare for it, I bought about 4 of the study guides (I thought I would study for months in advance and learn everything in all of the books--that didn't happen). The books I would recommend are:
The Evolve Reach study guide, this is the one they recommend on the website. http://www.amazon.com/Evolve-Reach-A.../dp/1416056351
I went through the entire book. In the few weeks before the test, I would work on the math and vocabulary. By the week before the test, I still hadn't finished though, because I didn't set enough time to study. So, about 3 days before the test, I skimmed through the entire book and took the practice test, then reviewed the information I was unsure of. DO NOT try to read the entire book. It is unnecessary and will not happen.
The second book I recommend is the Hesi A2 Secrets book. http://www.amazon.com/HESI-Secrets-S...8392453&sr=1-1
I really just used this book for extra practice the day before the test. The thing I like best about this book is it explains ALL answers. The other book just simply says the answer is a,b,c, or d. I took the practice tests in this book also, and my scores for both books were AWFUL...so I was very nervous. DON'T BE!! I eventually just decided to quit studying.
DO NOT stress yourself out the night before the test. Just relax!! I reviewed some vocabulary before bed, but it's totally unnecessary. I woke up super early, had a big breakfast, and got to the testing center about 45 minutes before my scheduled test time. I was SO nervous, but convinced myself I'd be fine. I was right.
Math- There is a calculator you can use on the computer. This is the section I spent the most time studying, because I forgot all the math basics. The problems I got the most of were the proportions. (ex: 1:4::3:x)
Vocab- This was my lowest score. I am good with vocabulary, but there are many words that even context clues can't help you find the right answer for! Just review the vocabulary in the books, though, I didn't flunk it, it was just my lowest score.
Grammar: TAKE YOUR TIME ON THIS SECTION! I thought "this stuff is too easy" and basically flew through it. I caught myself click the wrong answer several times!
Reading Comprehension: SUPER SUPER EASY! Nothing like the ACT where there are long boring passages and stupid questions. The passages are about 5 sentences each and are very easy to read and follow. The questions are totally straight forward and not at all tricky.
Biology- Basic concepts, I had just taken bio so this came super easily to me. Make sure you understand the basic concepts of Biology, it's not too in depth.
Chemistry- Again, basic concepts. Don't freak out.
A&P- I took A&P long enough to take the first test, and then I had to drop it, not because of my grade though. I thought the A&P section was pretty easy. Know the different planes...(is that the word???: sagittal, coronal, etc) know the different positions (supine, anterior, posterior, proximal, distal, etc.) know basic A&P concepts.
NO PHYSICS SECTION FOR THE HESI A2..DON'T WASTE YOUR TIME STUDYING THIS!!!!
Remember, BREATHE! It's super easy as long as you have common knowledge and prepare yourself appropriately
Sorry I typed you a novel. Hope I helped a little and let me know if you have any more questions!!