My most favorite and cherished kitchen tool is my meat thermometer. It cost next to nothing and it makes me a much better cook. No longer do I serve dry meat...or worse....chicken that is pink in the middle. I wish I had gotten a meat thermometer years ago.
Second tip, which I think is what separates good cooks from great cooks...don't be afraid to experiment with different flavors or techniques...variety is the spice of life and it keeps the family on thier toes!