I took the HESI A2 test a couple weeks ago. I did the study guide (HESI A2 Exam Review, 2nd edition) cover to cover.
The questions on the test were very similar to the guide and will give you some basic information on the types of questions, the wording and format of the exam. Make sure you study math - fractions, decimals, roman numerals, ratio and proportion, percentages, common household measurement, metric measurement, conversion, 24-hr clock.
It won't hurt to brush up on your grammar
I was not aware that the exam that I took was not going to include chemistry, biology, physics and A&P sections. However, tidbits that were in those sections were included in the grammar/vocab, math and reading and comprehension parts! So I did a bit of overkill on the studying part but I felt that the extra time didn't hurt.
I probably spent 10-12 hrs on the guide. I have posted elsewhere on this board about the exam. You may want to take a look.
Hope that helps and good luck!