Your first step will be to decide what you want to track. A good place to start is to look at how you currently are attracting clients, your income and expenses, what services (and products, if you have them) that are contributing revenue, and of course where you spend most of your time.
Next you want to look at expenses. What “fixed” expenses do you have per month or per year (for example, website hosting or email list software)? Do you pay for your own health insurance?
Last but not least, look at the amount of time you’re spending to generate your income. If you’re not already tracking your time, you should be. In particular, you want to track the amount of time you‘re spending on each client project, in order to make sure you’re pricing your services appropriately.