You must determine your passion first. I mean besides making money! What are your hobbies?
What do you know how to do it really well? What do you do? Everyone has something that is their own special talent. Find yours.
You may have more than one thing that you are very interested in and doing well. See if you can find five (ten if you are really ambitious). Write them in the list. Remember, you will spend a lot of time working with this subject. Make sure you enjoy it!
Lower each item in your list. Start writing an outline of everything you know about the topic. It doesn't have to be complicated. This is only to give you an idea of how much information is available for a particular subject.
Try mind mapping. Write down the main subject of your idea. Draw a circle around it. Now, start thinking about subcategories related to your main category. Make a line from your main category and end with a circle. Enter the subcategory title in this circle. Find as many subcategories (and sub-categories) as possible.
Go through each of your interests with this procedure. Choose the one that you know best and which you can write comfortably.
What if you "think" you don't know enough about your topic? Then, do research. Read books and magazines. Do some searches on the internet. Who knows? You might find a niche area, which is just waiting for you to fill it with useful information.
There are more affiliate marketing, of course. But the first step is finding your passion. "Excitement" You don't have to make money on the Internet. It can be cooking, sewing, billiards, or whatever. In fact, it's better if you find a niche that isn't in the online marketing arena because that's what almost everyone does.
Make your topic unique. Make it yours. And make your passion. This will pay you well.