Advice before you join that start-up, no matter what they promise you money, fame and/or a buyout.
Having been part of many start-ups over the years here's what I learned. People are key to success. That's it it's that simple, most start-ups fail not because the idea wasn't valid but because the people implementing it got caught up in their egos, control, and denial. Many start-ups rely on "free" or low-cost employees but how you're treated makes all the difference, free snacks and games aren't impressive.
If you're asked to join a start-up, I recommend, first and foremost ask for financial records before you commit. Google the founder/s and read what they've written or what's been said about them. Take any contract to be reviewed by a lawyer you trust. If you can, work with them part time and see how that goes, before committing. If you don't feel comfortable for any reason during your time working with a start-up, stop.
A lot of people get caught up in the "I'm an entrepreneur and working for a start-up" cool factor and ignore all the warning signs. Working with shady people also damages your reputation. Worse, though, is being taken advantage of and having to waste a lot of your time and effort on broken promises and people.
My career is anything but typical. I love technology and the digital world. After Silicon Alley imploded and sixdegrees.com, one of the first social media cos did so with it. I still wanted to stay in digital and explore how it could connect people and businesses to further communication. I convinced some technology cos, they were the only ones listening at the time, to continue and advertise online to brand themselves and sell their services and products.