Say you have just embarked upon a new data-centric web application project, is there a to-do list of common best-practice things you tackle before getting to actually solve the business problem at hand ?
Make sure your database design is very solid and well thought out. A well designed database can save a lot of aggravation later on as the project scales and gets more complex.
There are a lot of things to cover, but one important one is a good database design. You don't want to be half-way through the project and realize you need to make some changes that require you to update all those forms/reports/page you already created. Sometimes it happens, but the more you plan, the more you can avoid it.
At the same time, as you are determining your db structure, you can also be laying out how users will be interacting with it. A lot of times the way the users will use the data may require you to make database changes. We recently had a problem with that where the client wanted a small table created, but afterwards realized that to do anything meaningful with the data we had to triple the amount of information they had originally proposed to store in the new table.