How to Start a Profitable Ecommerce Store?

Firstly, you must have products to sell. You may need to put tremendous effort in marketing, list building and SEO inorder to generate traffic to your site. I also recommend introducing your product through reviews, blogs, social media or selling them on eBay and Amazon to funnel some customers or prospects before jumping into your own e-commerce site. The fact is nobody knows about your product and people initially don't care so let the people know about your product, make some noise, shout your product to the top of the world. If you have no popular brand, the process may take time... patience is a must.

I do not own an e-comm but have helped three of them so far and they are doing well, there are many things involved, from your platform to products to operations and store design and marketing and and and...
Here are some small notes from my experience:

1. Pick the right platform, it might seem that they all do the same thing but they are not, different security levels, different integration and so on. Good platform offer things that you might not think of in advance.

2. Think of your products you want to offer and the market very carefully, I suggest you do a PESTEL analysis or any environmental analysis before starting to spend money/time on things. Some ideas look really good in advance but fail to grab attention or enough market.

3. Store design is extremely important, think of your everyday shopping experience, you go into a supermarket and you know where everything is. The same applies to an e-comm website, your shoppers must be able to navigate easily. Also do not over complicate things with super cool design, the more thing on sight the less the probability of purchase.

4. Think of your operations step by step very carefully before you start anything, sort out the delivery of product or service way in advance. From when you receive the order to when it is released, there must be a process designed and written so everyone knows what to do.

5. Pick the right shopping cart which matches your payment gateway provider as well as your shop's platform so you do not need to work extra to put in the API

I hope this little insight helps you
Good luck

I would focus first on finding a SUB-NICHE that has decent DEMAND but manageable levels of competition.

This is where most ecommerce entrpeneurs FAIL.

They simply pick the wrong battles to wage.

Use Google keyword planner and Google's search engine to find traffic volume, CPC, and competing page volume respectively.

Next, I would focus on REVERSE ENGINEER related players.