Of course the answer to this question is dependent on what you do, but if you don’t start by answering this question you will miss out on opportunities. The answer, based on your line of work, may be a type or category of businesses or categories or people.
Some sales people think the answer is anyone and everyone, but it isn’t. On the surface, if you are in pharmaceutical sales it is doctors or medical practices or if you are a pool installer it is home builders or homeowners. It is important to start with the big picture and then narrow it down so you can come up with reasonable marketing and networking strategies. If you are the pharmaceutical salesperson, your company may assist with this by assigning you a region of a city, state or the country and providing leads. If you are the pool installer, you have to choose the geographical area you can reasonably cover with your crew(s), let alone the number of projects you can work at one time without causing delay and upsetting customers, before deciding how to market to your audience of potential customers.
Some professions, including attorneys, accountants and financial planners, have a different answer. We all have the skills to help many types of businesses and people, but a wise man I know told me something years ago about who your clients are likely to be, which still holds true today: look in the mirror. What he meant is that you are naturally going to connect to people similar to you, whether in age range, family background, interests, etc. We all know personal connection helps or causes us to make choices a lot of the time.
Where this leaves you is to remember, no matter your business or profession, you need to have a plan and strategy for your marketing and networking. If you have no plan, you have no plan, and you will have hits and misses, though likely more misses, because you are leaving your business to luck or casting too wide a net (a wide net has large holes for potential business to slip through!). It also helps to put your plans on paper, with short term and long term ideas, plans and goals.
If you start by defining who is your customer or client and drill down from there you increase your chance for success. So start today because there is no time like the present!