I started where you are, my first score was a 510 on my Mahnhattan practice exam. I knew ahead of time that I needed work in all areas as I have been out of college for 10yrs. I bought the set of 8 Manhattan GMAT prep books and the OG12. The second test I took jumped to 560 after just a little study. I am still in the process of studying and have 5 weeks till my actual exam. These books have been good for me as my basic skills are rusty. You'll need at least 3 months to go through this material with an average study time of apprx 10-15hrs a week to get through the whole series in my opinion. My target score is 650, not trying to get into ivy league schools but obviously I hope to get higher than my target. I have seen other threads that say Manhattan is a good program too.

jswiatek wrote:Anyone recommend a test prep? Right now, it appears that my scores are pretty bad high 400s and low 500s. Any advice?

For verbal, i will recommend e-gmat.
For quant, i will recommend mgmat guides.
For over all GMAT, more effort and right preparation strategy.
finding out easier/faster/different ways to solve quant problems.
redoing and reviewing both incorrect/correct question in practice problems.

Check out the Verified GMAT Course Reviews in the GMAT Courses section on this website. It is quite thorough.

Personally, I would recommend Manhattan GMAT.