A score of 24 suggests that you may have gaps in your foundation skills. So, be sure to find a learning resource that starts with the basics and slowly progresses to advanced concepts (I'd be remiss if I didn't mention that our course does this)

To improve in math, I believe that you should compartmentalize your learning and take the time to master each topic (e.g., percents, ratios, exponents, statistics, etc.).

This means that, for each topic, you should:
1) Learn the underlying concepts (rules, attributes, notation, etc.)
2) Learn GMAT-specific strategies related to that topic
3) Practice dozens of questions all related to that one topic.
4) Don't stop working on that topic until you have mastered it
Then, and only then, move on to the next topic.

I also suggest that you spend a lot of time reviewing the responses from the Experts on this site. They model the steps you should be taking when tackling math problems.

Cheers,
Brent