Never start a project in hurry, you are not a superhero who knows about all products exits in the world, give respect to design, understated from the start of products making process, visit the shop floor (if this option is available), observe manufacturing process, assembly process and how it going to use at the customer end, Spent sufficient time in studying the problems first. A clear understanding of the assembly process will help you in deciding the proper contact behavior formulations, Also clear understanding of functionality is essential for applying appropriate boundary conditions and help you in removing the unwanted part from assembly for FEA modeling.