The best way to acheive success is to plan for it.
When it comes to window and door weatherization, proper flashing design and technique are typically the difference between success and failure.
Challenges in the field may include large units, recessed units, arched heads, panning systems, material compatibility and the creation of an efficient drainage plane behind siding or stucco. All of these things can be addressed by designing a system of components working together to acheive the goal.