Following are the quotes which I often read to inspire myself To Be a Good Tester,
"To be an efficient software tester the person really has to enjoy testing, have a knack for it, be analytical, detail oriented, and be versatile, such as
a) Be technically savvy,
b) Understand the business, and
c) Never stop learning and improving on the testing efforts"
Think of at least three possible explanations for something that you've observed. If you can do that reliably, you're on your way to becoming a first-class tester.