GMAT Strategy

My question stems from me being out of school for 5 years and having poor results with the practice problems I did out of the OG book.

For someone that probably cannot even setup a basic problem, would you advise a prep course first and then self study during and after the course or would it be better to educate myself on the topics first so that I know what to ask when I attend a class?

I'm beginning my B-school journey and greatly appreciate any advice.

Thanks,

George