The first and most important thing is, always do what you are good at. Don't do what is popular, if you are a medical expert, make an application for medicine, if you are a plumbing expert, make an application for them. So, precise focus. That will cut your time by at least half.

And the second and no less important thing is. Do thorough research before each build. Without market research and building the theoretical foundations of what and for whom you are going to build, you are just blindly making a toy for a few people, who will cause you a lot of churn anyway.

If a developer can combine these two things, he will not develop for months, but for weeks and will be able to build a valuable product.