For starters, you need a good expense tracking system, a good hours tracking system, a good accounting system, and a separate business banking account.

You need to know how much time you spent doing the work (honestly!)

Whether working by the hour for someone else, or working on your own product, keep track of the time you spend on the projects you work on.
If you last job was paying you 1600 a week, and you are now working 12 hour days for the same amount of income, you are now making half ($26) of what you were paid before.
Tracking your hours is the only imperial way of improving your estimates on how long it will take you to do a custom job.
Tracking your hours is a way of being honest with yourself of how much time you are diverting from pursuing other opportunities (family or business).

You need to know what expenses you incurred producing the product

Keeping track of your expenses save you money: if its deductible, it will save you thousands of dollars in taxes, and if deemed non-essential in hind-sight, you'll  know what you can cut back on next year.

So Save every single receipt. Categorize them as best you can.

You need to know who you owe money to, and when its due.

You need a way to see what you've already committed to paying and when, so that you can predict what you've got left.

Take care of your suppliers and hired help. Pay them on time. Every time.
If you build a history of being a straight shooter with them, if you ever run into trouble, they'll probably cover for you as you re-organize.

You need a means to bill someone to get cover the above labor and expenses

Handshakes deals went out the last century. You need a way to clearly bill for your services and products.

You need a business bank account separate from your personal account

Its a pain, and another expense that impinges on your shoestring budget, but you absolutely need a separate bank account for your business expenses and income.

If you violate this rule you not only get completely muddy insight into your expenses, but -- more importantly -- you risk “piercing the corporate veil”, which means you risk loosing your business, and your house, and your car, and money, if you got into legal hot waters.

Trust me: if you can't afford to pay a monthly fee for a second bank account, you're too close to the line anyway.
If you plan to run a business, there is no excuse.

You need to keep it simple

Concentrate on what makes you money, and minimizing your costs, not on trying to become an accountant.

You need to carefully choose the tools that will make your input-ing of time and expenses an easy daily (hourly!) activity, and a means of importing them into your accounting system an easy, quick  monthly (weekly!) activity.

You need advice

You probably don't need an accountant when you start your company, but hopefully you'll quickly grow into needing advice.
When do you know? When the accountant can probably save you more time and money (legally) than you can by doing the books yourself.
In the meantime, you definitely should use a Tax Consultant for the year end, so factor in that upcoming expense.

Conclusion

No one especially likes accounting: designers would rather design, and programmers would rather code.
But it’s a necessity, and with the right tools, easy.