Small businesses don't have to compete directly with larger businesses (who don't normally target niche markets)
A small business selling microwave meals could establish a niche by specialising in meals for people with nut allergies - this allows the business to make a profit even though there are lots of large ready-meal businesses
Customers have a mental map of the market and will position new products relative to the alternatives
A business needs to look at where would be the most effective place to position its brand or product in relation to its competitors (e.g. if it can't compete on price or quality it might push the convenience or ethical nature of the product)