Foremost, it depends on the kind of business you have (model, in which industry, what it offers, your goals and so forth).
The simplest way to find competitors in business is Google. Use different variations of keywords to search. You will get different results. Visit individual websites and check out their products and 'About' page. Then create a list of all those businesses that you think are your competitors.
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But that's a generic way. Let's get into more details…
Per your bio, you're into matchbox manufacturing. And your website (if I checked correctly) says you're based out of Madurai in Tamil Nadu, India.
Now, you want to find out competitors in business. Use Google Advanced Search.
It includes many (optional) fields that you can use to filter out the results per your needs.
Put in the keywords under "Find pages with"…
The words and phrases you want users to search to find a business like yours, the numbers you would want your results include, and the words that you don't want to show in the result.
Then following, narrow the result based on the language, region and more.
So, for example, if you’re looking for competitors in India, put that in the region area. And then choose other options per your need.
I did this. Here are the names of your competitors in Business that I came up with:
• Quenker Matches
• Adhi Sarraf International
• Nizam Matches Pvt. Ltd.
• Asia Match
• Prabath Match
• SS Multinational
• Renga Matches
And there are MANY…
This way you can find many of your renowned competitors in Business rather easily.
Then, of course, you can use different directories like Indiamart to find your competitors.
In the end, it all happens on Google.
Hope this helps.