Online services and software like Xero, Freshbooks, MYOB, and Quickbooks can be a godsend when it comes to keeping track of everything you’re doing. You can hook most of them up to your bank accounts too, which means you can just login and see all of your incomings and outgoings in one place. Even your accountant can login and keep tabs on you (which, although it doesn’t sound like it, can be a good thing).
I couldn’t recommend those programs enough – but maybe you find it easier to use Microsoft Excel or Google Sheets and punch everything in manually, or maybe you’d rather do it in a notebook. Everyone works slightly differently, so find a way that works for you.