First: the best is the enemy of the good, trying to be perfect or trying to meet infinite context will both make you crazy and make you miss your launch date. The only thing to do is to create a product for your users. Not The User but the specific audience for whom your product is intended.
quoting Voltaire best is the enemy of the good
You ask about the important things to keep in mind: same as ever, with a task-based twist: what are the users trying to accomplish, what does the business need them to successfully accomplish, and what will the technology allow? If you can balance these three forces, you'll have a solid product.