Without details, it's hard to provide specific, tailored advice, but here are some general tips:
1. Be sure to try out unusual values (e.g. fractions, negative numbers, zero, etc.).
2. Make sure you don't carry information from one statement to the other when you are checking each statement individually.
3. Stay focused on what the question is asking (sounds obvious, but you'd be surprised).
4. Don't forget about information in the stem. It's a good source for clues (e.g. "If x is an integer..." don't try non-integers, but do try negative values).
If you want to provide some details, I'd be happy to offer more specific advice.
Economist GMAT Tutor