Here is my tip #3 for successful online niche store: BELIEVE!
You should really believe in what you are doing. You should also believe in your success. If you do something just because somebody said so or inspired by a blog post or the news you are most likely to fail. Every business is different so should be yours. Do not just copy what other people have done. Create your own routine and follow it. Here's an example of vintage fountain pens online store. Browse categories and products and see what seller has done to attract buyer's attention.