What are some pitfalls a developer should avoid when developing the first SaaS product?

Avoid to:

• Build something that wasn't validated
• Overengineering/overoptimize
• Keep on building and postpone launching

All the other answers so far have been great.

I'd also avoid:

• Building a product first, then thinking about how to market it. Instead, design your landing page and marketing material first. Get feedback from real customers, then define your MVP.

• Working on scaling problems, such as architecting your application to support thousands or millions of users. None of it matters in the beginning and trust me, it's a good problem to have later down the road.

• Speak to potential customers often
• Join niche forums where your target audience hangs out
• Build an MVP https://blog.crisp.se/2016/01/25/henrikkniberg/making-sense-of-mvp
• Target a good market (big/growing)

1. Develop your MVP like how you would work for a big company. To achieve the MVP sometimes you need to take shortcuts., not-so-ideal solutions. If people start to like your MVP you still have time to refactor the code.
2. Not solving your own problems. If you want to be passionate about what you do you need to solve a problem in your life.
3. Not keeping deadlines and always postponing the launch.
4. Hoping that whenever you ready to launch it will be enough to post about it on Product Hunt, Indiehackers and similar sites. Gathering a group of interested people before launch is mandatory.

1. Expecting your first attempt to succeed.
2. Spending more than 10% of your time writing code / working on product. Talk to customers instead.
3. Building something nobody is asking for / searching for (not only should they want it, but already be looking for it. You don't have the funding to teach them about a new thing).

Just building it, no matter how good it is, doesn't mean people will find and use it.

Get something in front of potential users first.

Don't fall victim to the scope creep. Define what your MVP should be and stick to it. Once you've launched it, then you can build out additional features (assuming end-users actually end up wanting them).

I'd echo what others are saying. The two biggest pitfalls, in order, are:

1. Building something that not enough people want.
2. Launching too late.