I'm talking about specific tricks, not generalities. I'll start things off :
Phone lines - Rather than setting up expensive business phone lines for all the desks in your office, use Skype. It’s free to connect with other callers within the Skype network or you can use SkypeOut to make unlimited domestic calls to those who don’t use Skype for $24 annually. Alternatively, MagicJack also lets you make free domestic calls on traditional phone lines. All you need to buy is the $39.95 jack, which plugs into your computer. After a year, renewal costs just $19.95.
Payroll - a tedious but necessary task. Rather than hiring someone to do this in-house, outsource payroll to services like paycycle.com and save both time and money.
Please add to this list.
Then stock the place with enough coffee, tea, energy drinks, water, bread, cans of tuna, cans of soup, whatever that's fast and doesn't go bad so you don't have to go out if you're in a good flow. Instant coffee also potentially saves a hell of a lot of money if you're a coffee drinker and on a tight budget.
Edit: Another thought - if you wind up hiring any accountants or lawyers, be really, really cool with them. I remember I hired a lawyer to look at an important contract and I asked his secretary how he took his coffee. That combined with being friendly and gracious went a long way - we originally planned to go about an hour, we went two hours, then he only charged me for one. Very helpful guy, too. Being friendly, courteous, gracious, and doing little gestures makes people want to take care of you. When you don't have money, you have to think even more about being appreciative and putting your time to use for other people.