I highly recommend using an accounting package, even if it's just quickbooks online. it helps so much when it comes to tax time.

For my business we use Xero so we can track expenses against the income for tax purposes.

Are you tracking hours so you can confirm your hourly rate? I use a tool called Toggl for that although there are others.

you can look at your bankstatements and focus on your cash flows in, then project those out.

Also, try to get 50% upfront wherever possible, especially if you have to pay others. Because that last payment seems to drag out a while....

Let me give you an example.

Assume, your monthly target is $1,000. Now, you are taking 30% upfront money. So, if you able to get $3,500 projects a month then you can able to get 30% upfront money that equals $1,050. So, you can fulfill your target.

Here the key is buffer projects and you need to set milestones with buffer timeline. So, once you get the first 30% then target the next milestone or 30% to get within 20 days time. Then, even if client delays you still have buffer time.

Hope this will help you.

I can't speak to whether or not it's good, but I think http://cushionapp.com/ is a really nice idea in terms of helping freelancers track and manage cash flow. Wish I'd thought of it :o)

Quickbooks online self employment edition. It tracks income, expenses, and does quarterly taxes for you.