Just about every topic that you can imagine is published on the internet.  This makes it difficult when a client tells us that we need to find a unique angle, but it is not impossible.  A little creativity and looking at what you already know about the topic at hand can help you craft an article that has a unique flair.
Your Life Experiences
Personal experience is always unique.  You won't have personal experience with every topic in existence, but it is inevitable that you have personal experience with several dozen things.  Have you done your own repair on your vehicle lately?  Have you had an MRI done?  Have you tried a new beauty or grooming trend?  Write about this stuff.  Folks surfing the web enjoy reading about what other people experienced with something they have either tried or will be trying.  Not all clients will accept first-person experience, so keep this in mind, but many will and many will pay rather well for it.
Use a Single Element of the Topic
Every topic has a variety of elements.  For example, roof repair and multiple sclerosis are two very different topics and when you look at the bigger picture you will see that dozens of narrow articles can be done on each.  In terms of roof repair, you could talk about choosing the right shingles for your geographic area, whether nails or staples are the best for your shingle type and how roof slope affects the cost of labor.  These are just three topic ideas generated from the very broad roof repair.  With multiple sclerosis, you can break this down into dozens of articles.  Some examples include writing about how plasmapheresis helps in treating this condition, the pain related to MS and natural ways to cope with the MS hug.  The best way to narrow down is to take a topic and analyze it.  Think about the subheads you would use in a broad article and make each subhead a single article.
Choose a Specific Audience
An article that looks at getting more fiber in your diet has been done a million times, but choosing a specific audience for this can narrow things down.  Most articles on the above topic are targeted at adults, so why not write about how to get more fiber into your toddlers' diet.  Keep the article focused on toddlers only.  Talk about how much fiber they need per day, foods that toddlers like to eat that contain fiber and how to sneak in fiber when they are not wanting to eat those fiber-rich foods.