[qhoang09]

Lots of great answers here. I'll just add, as a founder myself, that things will probably not be very structured at that stage.

That means you may find yourself working on very different things every day, maybe even things outside the traditional software developer role. (For example, you might be asked to help on customer support). Be open to wearing multiple hats and being a team player.

Also don't expect to get too much direction. You'll need to be a self-starter and autonomous. In fact, I encourage you to take the initiative and even lead projects. There's no better way to hone your leaderships skills than at an early-stage startup.

Finally, don't think of it as a regular job where you clock in at 9 and out at 5. You may not be told explicitly to put in extra hours but if others are doing it you probably should too. You are a part-owner after all (if you're getting equity).

That being said, don't forget to take breaks and recharge!