Avoid NSAIDS (Non steroidal Anti Inflammatory Drugs). I have gastritis, too. Definitely follow the GERD diet. You can try DGL (found in supplement stores) if you actually experience burning. I found it unhelpful myself. No coffee or real tea. Mint is irritating. Citrus may bother you, too. No canned tomato products. I think you can see the trend here.
You might want to check to be sure you're not harboring H. pylori, a bactera that is implicated in causing gastritis. Also consider following a GERD-friendly diet. You can find a representative example at www.gicare.com.