Here are a few rules for happiness that I have learned (often the hard way) running a solo software business since 2005
Make sure your important stuff is backed-up automatically
Any sort of manual back-up is going to get forgotten. Back-up to more than one place, at least one of which is offsite.
Stay away from the bleeding edge
Use good suppliers
You need your hosting company, payment processor and other critical suppliers to be rock solid. Think twice about going with a supplier just because they are cheap. Changing suppliers can be a pain, so ask around before trying a supplier.
Use version control for everything important
It matters less which version control system it is. Periodically making a copy of your source folder is not a version control system!
Don’t promise ship dates
Developers are notoriously bad at predicting dates. If you promise a date and get it wrong (and you will) then you either have to miss the date or cut corners. Neither is good.
Never send an email you might later regret
If you are starting to feel angry writing an email, then stop writing. Come back to it later. Or maybe write it, feel a bit better, then delete it without sending.
Write documentation as you go
Few people enjoy writing documentation. But if you leave all the documentation until you have finished programming, then you are likely to rush it and forget stuff.
Have a checklist
Automate where you can. Have checklists for everything else. Keep updating your checklists.
Get someone else to proof read everything
Typos are embarrassing, but it is impossible to proof read your own stuff. So get someone else to proof read any stuff that customers see: web pages, newsletters, documentation etc.
Never release changes just before going on holiday
You don’t want to have to be fire-fighting a new bug when you should be on the beach with your family/friends.
Don’t try to do everything yourself
You could spend weeks learning about taxes, web hosting, CSS or any number of other topics that aren’t central to your business. But why bother? Pay someone who already know this stuff.
If you wait for perfection, then you are never going to ship anything. Just make sure each release is better than the last. Good enough is good enough.