There are lots of things that need to be considered before going into designing a logical and physical data model. We must consider FIRST what type of data we are going to store, how the data is being accessed, understanding system playing the role of upstream, understanding downstream system and finally planning by understanding volume of data that is going to come on a daily   If we are going to upgrade any existing platform then understanding existing pain area also help developers to design the database to meet future needs along with remediating those bottlenecks.Understanding your data is important but unless we have CLARITY of different components of data, we would not be ABLE to make a better plan.

Also, we need to revisit our design at several stages of a project as we work in an evolving WORLD where requirement changes overnight. So Agility and flexibility of database design are very important. We should be able to meet any future requirements as well with a flexible approach. We should always revisit data relationships, volume and indexes to ensure we stick to the flexible requirement. Also, we should always frequently profile our database server using tools like SQL server profiler to identify any problem areas on a regular basis.