Some factors to consider in defining these goals are 1. It doesn't always happen quickly, and you'll probably need to adjust things and experiment a little at first. It is very important to think about your intended audience at the onset of the project because your application must effectively target your market. Consider how your market can benefit from your presence. You must create a realistic budget and timeline before starting an electronic presence.
Projects can fail if they start out with large scale goals, but limited budgets and timelines.
The best way to avoid this is to adopt a phased production approach. Keep the large scale goals as a final target, but develop smaller pieces of that vision incrementally and hold on to the other pieces for later phases. This is also a nice approach to give colleagues a chance to get familiar with the Internet and how it works. Once the site is up and running, feedback can help shape the product and determine efficient directions. It's important to include enough functionality into early phases to simplify the implementation of the later ones.