I would pick up a copy of the Elsivier hesi study guide and pay special attention to their "tip" boxes.
For the A&P section know your hormones, their origins and functions - i went here and made flash cards based off of what the website says for each hormone/gland Edno 101: Endocrine Glands
Also study the heart- the valves, chambers and the direction of blood flow. Also know the origins of blood through arteries and veins.
Math is a lot of probability and percentage to decimals.
Go to Simple free learning tools for students and teachers | Quizlet
and search Hesi. This will bring up a lot of good reviews. You can also search specific subjects. And they have different "games" to help you study.
The vocab in the elsivier study book helps a lot, so create flash cards for those.
I studied for about a month before hand starting with the subject I was most fearful about. I moved onto the next section once I could answer questions without flipping over a card or could map things out on paper and label them.
I got a 98% overall on my Hesi and a 850 in critical thinking.