Competitive analysis
During the planning stage for a site you should be researching other sites in the industry sector. This allows you to see everything that others are putting on their sites and keeps you from accidentally forgetting something that is an important part of every site. Seeing the successes and failures of other sites will help guide you in creating your own.
Working together
It is important that everyone you are working with to create a site is on the same page. You should be speaking with your client and colleagues to plan what you want the parameters of the project to be. Great planning comes from collaboration.
Planning Checklist
The first part of the planning checklist is to collaborate with the client and understand what they want in their site. The second step is to determine your audience. The third step is to come up with a budget with your client. The fourth step is to make sure your site is easily accessible for everyone. The fifth, and final, step is to extend your planning for the future of the site, and not just getting the site up and running.