The second time you work with a design element, modify the design to make it more general—but only general enough to solve the two problems it needs to solve. Next, review the design and make improvements. Simplify and clarify the code.
The third time you work with a design element, generalize it further—but again, just enough to solve the three problems at hand. A small tweak to the design is usually enough. It will be pretty general at this point. Again, review the design, simplify, and clarify.
Continue this pattern. By the fourth or fifth time you work with a design element—be it a method, a class, or something bigger—you'll typically find that its abstraction is perfect for your needs. Best of all, because you allowed practical needs to drive your design, it will be simple yet powerful.