Update your installers
Another easy thing to do is update your installers. Even if the software you're installing is pretty much the same as you've been selling and updating for years, that installer that is sized for eight-character file names and likes to stick things in the root C:\ directory is going to seem completely anachronistic.
There are some great, free installers out there. I know it's another weekend's worth of work, but you do want to keep your company, don't you?
Update your system requirements specs
If the last OS listed in your system requirements is Vista, you have a problem. If you list NT in your system requirements, you have a bigger problem.
Test your product against Windows 7 and Windows 8, and then update your system requirements to explicitly call out that the product works on Windows 8. Don't worry about the idiotic "Metro" interface, but if you say you support the Windows 8 desktop (and you do), then your prospective customers won't think you've been in suspended animation since the Bush administration.
Post a frickin' phone number
Yeah, I know we're moving to a world where all interaction is online. But customers who want to buy stuff sometimes want to call and get an answer to a question right now.
I also know that posting a phone number is an invitation to your current customers to call, bitch you out, and ask you questions you can't answer, but that dialog is good, too. It'll reinforce to your customers that you're still there. Plus, you never know. That really loyal (if cranky customer) might just have a way to save your bacon -- simply because he needs your product as much as you do.
Acquire some other products
Most of the software tools vendors I've seen are one-trick ponies. They have their one product, and that's it. That means if you make a sale to a customer, you're done. There's no more money to be mined from that hole until you release a major update.
One great way to augment your income (and help maximize utilization of the business infrastructure you already have) is to acquire publishing rights for other programs. This isn't quite as easily done now as the days when distribution meant brick-and-mortar and manufacturing meant paying for packaging, but there are still a lot of talented programmers out there who don't want to do the administrivia.
Don't contract out to have something built. Instead, scour the Internet for great programs with poor descriptions, support, or web sites. Offer to publish those products, update the manual, sell them, and provide a royalty back of 15-30 percent after your cost.
You'll probably need a contract to do this, but don't go running to a lawyer. First, most lawyers don't know squat about the software business, and you'll wind up paying more for the contract than you'll make selling software. Instead, find another software vendor who isn't a direct competitor and ask them if they've got a publishing contract they don't mind you using.
Make friends with other software vendors. These sorts of mutual-support contacts are very helpful.
I know you may not think you can afford to acquire a product, but trust me, it can be done. In fact, I wrote two chapters on this phenomenon in two of my books. Read the first chapter in The Flexible Enterprise and read "Luck is a skill" in How To Save Jobs. Both are free downloads, so there's no excuse not to.
An even easier approach (although a little less profitable) is to resell other existing products on your web store and in mailings to your existing customers. Find complementary (or even competing products) that would appeal to your class of customer, do a deal with the software vendor to resell it (you'll usually get 40 to 60 percent of the selling price).
Do yourself a favor and start this process now. An extra five or ten SKUs will do wonders for your incremental income.
Know when to hold 'em, know when to fold 'em
Finally, we're at the tough love stage of our discussion. Sometimes, it's just time.
Look, if your product really hasn't been updated since 2005, if you can only run on 32-bit XP, and you crash constantly on 64-bit systems or anything running Windows 7 or later, it may be time to throw in the towel. This dog won't hunt anymore.
There are lots of ways to get out of this hole, but all of them involve a change in business strategy. Again, I'll point you to some great reading. Read the third section of How To Save Jobs. It will show you how to evaluate your assets and reinvent your business from the inside out.
Live long and prosper
I sometimes get the urge to go out and build another software product. I love to code and I actually love the entire chain of activity that is product marketing. But after more than two decades of running my own software and then publishing company, I also needed to get a life.
I was fortunate in that I was able to sell off my software assets back in the day, and have managed to transform my career so that I get to talk to you here on ZDNet, lecture, advise, and teach. I'm having more fun in my work life than I've ever had before, I get to spend time with my wife, enjoy my car, lift weights, and sometimes work on my house and hobbies.
The point is that there is life after software. While my advice here is intended to keep you in business, if that time comes, you should know that there is life after software entrepreneurship.
Good luck. Live long. And prosper.