It's not easy though. Assuming you have product/market fit (i.e. something that sells):
Reliability is paramount. It is everything to you. If your system breaks, it will stop new development, marketing, support responses, sales calls. Because there is only one of you, you can't afford to spend time fighting fires and answering pages. It does not matter if your software is slow or fast or if it is pretty or ugly or if your userbase is growing or not if you are down.
Reliability is paramount. Invest your time into building systems that do not fail when one component or one machine breaks. Where you can, you should leverage primitives and services from cloud providers that provide the kind of failure guarantees you need. Then assume that your cloud providers will eventually fail on you, so design with that in mind. Take as few dependencies on them as you can handle or make sure you can failover between them.
Reliability is paramount. Every change you deploy could break your systems and cause downtime. You need good testing and monitoring. Run continuous end-to-end testing of all customer-facing functionality that pages you when it fails.
Reliability is a feature if your software is critical to your customer's business. Some will notice when your competitors are down and you aren't. For those that don't notice, educate them. Explain to your customers the investments you've made to keep your service up and running. You can sell it as a differentiator.
After that, support is the next time-sink you need to eliminate. Treat every support request as a bug that can be fixed so it doesn't happen again. Make it extraordinarily easy to contact you and then try to optimize so no one ever contacts you. Invest in your UX. Your UX should try to illuminate the inner workings of your software. Many support requests are simply failures of a customer to understand what your software is doing and why. Customers can't debug black boxes, but they are smart and motivated and if you invest in their understanding, many will solve their own problems before contacting you.
Design your error messages. Your error messages are a more important piece of design than any other messaging from your product. Finally, if you can't solve the support bug with UX, invest in your documentation. Documentation is your last resort because most users will not read it or they will only read portions of it. By the time they get to the docs they're already frustrated, so it needs to be fantastic.
> By the time they get to the docs they're already frustrated, so it needs to be fantastic.