I have a couple of techniques. I am writing in different venues for different reasons. In my day job as a consultant, I am writing content for client deliverables or working on white papers to enhance my company's business. In my spare time, I am blogging on technology trends and opinions about the industry. I can get stuck a lot where I am just drawing a blank. So I usually try switching projects. If nothing is coming for a work project, I switch to a personal project and write a blog post on something totally unrelated. When I am really uninspired, I go for walks and take photographs in different parts of the city.