At this stage you should be starting to feel like a master of entrepreneurship experiments, things are working and you are solving problems for customers. You have all the big rocks in your business model sorted out and now it is time to make small but powerful optimisations.
There is a LOT to learn at this stage but a great place to start is to figure out which experiment you should be running when.
When to Use Which User-Experience Research Methods
The field of user experience has a wide range of research methods available, ranging from tried-and-true methods such as lab-based usability studies to those that have been more recently developed, such as unmoderated online UX assessments. While it's not realistic to use the full set of methods on a given project, nearly all projects would benefit from multiple research methods and from combining insights.
Rather than going through all of the potential experiments you could be running I will just leave a breadcrumb trail of useful links for you to explore when you need.
A/B testing (also known as split testing or bucket testing) is a method of comparing two versions of a webpage or app against each other to determine which one performs better. AB testing is essentially an experiment where two or more variants of a page are shown to users at random, and statistical analysis is used to determine which variation performs better for a given conversion goal.
A Refresher on A/B Testing
It's all about data these days. Leaders don't want to make decisions unless they have evidence. That's a good thing, of course, and fortunately there are lots of ways to get information without having to rely on one's instincts. One of the most common methods, particularly in online settings, is A/B testing.
Better User Research Through Surveys
Online surveys are commonly used by marketers, product managers, strategists and others to gather feedback. You've probably participated in some of these surveys and I'm sure you've noticed that they're often executed poorly. Surveys are increasingly becoming a more accepted tool for UX practitioners.
At this stage you have done a lot of interviews but there is probably more to be learnt and perfected
User Interviews: How, When, and Why to Conduct Them
A user interview is a UX research method during which a researcher asks one user questions about a topic of interest (e.g., use of a system, behaviors and habits) with the goal of learning about that topic. Unlike focus groups, which involve multiple users at the same time, user interviews are one-on-one sessions (although occasionally several facilitators may take turns asking questions).