Create a blog about a niche and write about that topic. Write reviews about Amazon products (that way you earn affiliate commission 4 - 8,5% per sale). Also you could have your own store (astore) with your branding.
You could also have products on sale - take the list price and sale price from Amazon and let people know that you have the best price online! Also a nice feature: have the Amazon reviews from a specific product on your site. Then forward them to Amazon. To get the products you can use their product advertising api.
Most important is targeted traffic and content, so get started with content first! Getting the trust of your readers/buyers is harder than you think.
Amazon is great for the beginning and most people are comfortable buying on Amazon. But I don't like Amazon that much anymore. Their rules are too strict and their payouts are low.