Tracking your work is important. This means, what you need to be paid for, invoices sent out, etc. It could be you use something like oDesk, they may track your time, but you still want to have something where you keep track of the money from these particular projects, etc. You also need to have a tracking sheet of all the invoices you send out. If you have clients you have gotten that does not pay you through something like oDesk, you need to know what invoice you sent them, how much it was for and when you sent the invoice to them. Also knowing when you got paid is important. This will help you know if you need to follow-up on payments, etc.
You need to find what works for you. What I have used has evolved over time. I seem to tweak it the longer I freelance. The idea is to make sure it captures what you need it to so you know what is going out and what is coming in. If you don’t you won’t be able to do taxes correctly nor will you really know what you are making, spending and if it is worth your time to do it or not.
There are many different types of templates out there, so find what works for you. The reason for so many templates is because what works for one person may not work for another. It is always a good idea to make sure you know how it works for you. Don’t be afraid to ask questions about how it was set up, etc.