These are my 4 personal factors to co sider and use when a business idea is a good opportunity:
1. Supply and Demand in a market:
If you see an increase in demand (the willingness of a consumer to purchase your product) then this is the right time to start your own business.
If there is a large supply of a product, then it is the right time to sell the products before it gets caught up by competitors. If, in this case, demand is less, then you must focus on the system of the business, as this is the most important factor for the succes of the business.
2. Less competitors
If there are less or no competitors, I think this is your only opportunity to get monoploy (means that your business is the only one which can sell a specific product) if you business succeed.
3. Unusual/rare product/service
Bringing new products to the markets can bring you a plenty of money, if the product is new and unusual in your world.
4. Much workers
If there are many unemployed workers in your country, this is your opprtunity to stat your own business and hire them for the cheapest price. (As there is a increase in demand to work by workers, chances are that you'll hire them at cheaper price, because there is competitions between the workers)
I hope it helped you!