Who are your direct and indirect competitors? You really should gain at least an initial understanding of who else is offering similar products or services to your target market. It's good to know how their products or services are currently used and perceived _ why people buy them, and why they don't. In doing so, you begin to understand the strengths and weaknesses of your competitors from the consumer's perspective. Depending on what your product or service is, you can find all kinds of information about user experiences with your competitors' offerings. Sites like Amazon let you see product reviews by customers who bought products.
If you develop a good Profit & Loss Statement for your existing business for the current year or for the first year of your proposed business, you can use this data to actually project how much sales you would need to yield the income you want and the profit margin you want. You can plan ahead as far as you want. Sound impossible? It's actually pretty simple and can be pretty accurate plan.