It is important to know who you are writing for prior to brainstorming and writing. Your topics and tone will be very different based on who you might be speaking to.
Try to think of new fresh ideas to write about on your website or a new perspective on things that you have read about.
Choose a general topic and write very specific articles about it. You are creating more value to your users and the search engines by being specific.
Create a forum or allow for commenting to create a community on your website. If worried about people posting inappropriate things being posted to the site ensure there is some sort of moderation.
Create an editorial calendar to keep yourself on track with topics. Some systems will allow you to postdate your entries so they can be spaced out instead of having to publish an article on demand.
Categorize your posts so someone interested in a specific topic, can view topics specifically they might be interested in.
You are not only writing for humans but also writing for the benefit of being found via search. Be sure your titles are keyword heavy. Search engines like articles that go further in depth.