The best actionable advice I can give is to "emulate and innovate"
Don't try and reinvent the wheel but instead go into the market and see what is successful already and has proven itself to have a demand.
You don't want to be a trailblazer trying to create your own niche ... copy the ideas of the people before you and improve on it. Put your own spin on it....or just fill in the holes where they fall short e.g. advertising, customer service
Do your marketplace research and learn to spot ideas that make money and reverse engineer the reason why that is. See if you can improve on what they are doing.
Let me give you 2 examples which you could put to work straight away
Lets say you wanted to build apps for the apps store...most people would want to create something that noone else has ever done or thought of before.
The smarter way to do it is to look in the app store and see what apps there is always demand for. You'll spot trends which show where the demand in the market is. For instance you'll see alot of gaming and camera apps which are always in the top 10.
In these niches there is room for many players...dont assume you cant compete.
If you wanted to build a camera app the best thing to do would be to research what apps are consistently in the top 10 or 20 on the app store. Research there marketing, understand there product, and read the reviews on the app.
See if you can spot any negative reviews ... use these as ideas of how you can make a better product and improve on what is already working.
Another example is if you wanted to get into affiliate marketing.
Why start from scratch?
Analyse the market. See what ads and offers other affiliates are promoting and how they are doing this to understand what is in demand and what works
For instance use a competitive tool like whatrunswhere.com and see what affiliate ads are consistently showing up in volume for months on end. Hone in on these campaigns to see there processes....where they are buying traffic...and reverese engineer there success.
I've given these 2 examples as they are both location independent niches. Lets say you wanted to do something in the software industry...you can go through the same process.
Research to see where there is demand for software already....what software is popular atm that you can improve on?
Or another idea....read a site like techcrunch to spot new ideas and see if you can port an idea that is working already and proven to a different niche or country
Here is an example..."A spanish version of taskrabbit"
http://techcrunch.com/2013/05/29/etece-series-a/
Focus on building upon the ideas of others. Hope that helps