How do you get your very first customer?

Direct outreach. It's ok for the first customers to be achieved via non-scalable technics. In fact, the goal of getting your first customers is to find people with the power of bringing new customers. Your first target audience might even not be the future repeat-customer audience, but someone who can influence you future audience. For example, you build an app that students might find useful and increasing their productivity. But they might not be interested in increasing productivity, because students are interested in other things, but not really studying. So, you approach their tutors and professor. Explain them how this will save both teachers' and students' time, and sell this idea to at least 1 teacher. Teacher has the power to push his 20-30 students into using your product, for example, for creating and checking homework. It's just a new formal standard for interaction - using your app. Once students start using your app regularly during the course, some of them might find it really handy and useful - in case you've built a good product. And they start using it even for other courses and outside studying, for example. You then build this user-case as a selling point for marketing and future direct sales to other universities, and then scale it into marketing strategy. But for the very first - you can and should use quick, cheap and not exactly scalable solution, because it's a quick try and err phase.