I've been building web apps for 6+ years. Here's the single most valuable lesson I've learned:

Don't build what people ask for. Build what solves their actual problem.

Early on, a client said: "I need a custom chat system like Slack."

I asked three questions:
Why do you need real-time chat?
How will your users use it?
What problem are you trying to solve?

It turned out they just needed a simple notification system. What they asked for would have taken 3 months. What they needed took 1 week.

Here are the 3 questions I ask before every project now:

1. What is the single most important action a user will take on this page?
   If you can't name it in one sentence, you're not ready to build.

2. What happens if we don't build this feature?
   If the answer is "nothing much" - skip it.

3. Can we launch without this and add it later?
   In 90% of cases, the answer is yes.

This approach has saved my clients thousands of dollars and months of wasted time.

Here's a full case study of how I applied this to a learning platform I built:
Case Study

The full portfolio: Shahzaib