TC,
I recommend that your very first step be to take a diagnostic test, ideally at
www.mba.com. Why? Because GMAC are the test makers so theirs the closest thing to what you'll really be taking. Your performance on this diagnostic will identify/provide the following data points:
1) how you FEEL while taking the test and about the duration of the test (your stamina)
2) how you SCORE - both in terms of numerical score and where your current strengths and weaknesses fall on the spectrum
3) the SUPRISE/NO SUPRISE factor between 1 and 2
From the results of the diagnostic, you can then determine the best method, for you, of meeting you GOAL score which is likely aligned with schools you're wanting to gain acceptance to as well as your history in how you best improve upon your natural skill sets. How did you study for the SAT/ACT if you did study at all for it? What worked what didn't?
I don't recommend you study first, which Rich and others say/will say as an option...mostly because this diagnostic is a baseline score, a snapshot of how you'd perform right NOW and TODAY if you took the test. While you'll familiarize yourself with content and question types, pre-study is the equivalent of going on a diet but not weighing yourself prior. And it could be a rabbit hole in learning grammar, dealing with time managment, reacquainting yourself with 7-9th grade math. Just do it and know you'll likeley improve immediately.
It will become obvious fairly quickly that you're rusty (or not) in certain areas and the gains made by a little familiarity will skew how much you might impove, plus there are many hours of things to do to get (most) students up to speed.
The main thing that is different from 'real life' is the quant data sufficiency questions...which could be a brain twister if you're not familiar with their format, but compleletly doable. Many people taking the GMAT see this format on test day for the first time, so you're already ahead of the game doing this 'diag' beforehand.
Once you complete the diagnostic, and spend some time reviewing what you did know, what you're suprised you knew and what you flat-out didn't know, come back to the forum and we can all give you our feedback on next steps for score improvement (if you need it). This might include:
1) DIY study alone with the many resources available through people and organizations here and online
2) Group courses which are often solid solutions however deliver in a one-size fits all way. These typically provide a soup-to-nuts exposure of everything GMAT but typically don't include your specific needs and cannot always provide a kind of fine tuning that comes with
3) Individualized/one-to-one tutoring. This is typically less total hours for a student but not necessarily more economical. Still, if time is of a greater value to you and you want to focus on what YOU need to do to improve your score, this would be the way to go. For example, a course might be 30 hours, whereas, 1-2-1 can be anywhere from 5 - 20 hours total, depending where the students is starting out and where they want to go.
4) I also recommend you check in to review your history with taking tests, because knowing the material doesn't always determine top performance. The GMAT is not only about what you know, but how well you take tests...so strategy, critical thinking, time management and your 'mindset' will determine your performance and score...so how you 'score' yourself on this and recognition if you need support in these areas could catapault your score. For example, we worked with a student ONLY on his mindset, for 5 hours, and his score went up 230 points in a weekend. While this is atypical, gaining 50-100 points for just feeling confident and focused when taking the exam is fairly common with our students.
You'll want to set up a time line as to WHEN you want to take TWO tests - - most students take the test at least 2x, so what does your calander look with this in mind as well as what Round you're applying to, and when your ap(s) are due.
Look forward to hearing more about your process, goals and performance.
Good Luck!
Best,