What are GRE math tips and tricks?

Skip strategically (don't burn 4 minutes on one question when you could get two others right instead). Test answer choices by plugging them in when algebra gets messy. Estimate when exact calculation isn't needed. On Quantitative Comparison, simplify both sides before comparing. And always re-read what the question is actually asking before you submit. Many errors come from answering a slightly different question than what was asked.