Let's say I have a unique idea that can turn into a product for a particular start-up that works on a closely related technology. What is the best way to approach them and share the idea with them and get credit for the idea as well?

The best way is to polish your resume, go off to the startup and then apply for a job there.  They get your ideas, you get cash/money and some credit. The other way which is more complicated is for you to start your startup and then sign some sort of contractual business arrangment. One thing that you have to realize is that ideas are worthless.  You are likely to find that your idea has already been thought of, and they can't do it because of reason X, Y, and Z. I've found it's better to just give ideas away, and hope people "steal" them.  Ideas are worthless, but having people not put your e-mail in the spam bucket is valuable, so I've found just getting people that are willing to talk to you is worth giving away ideas.  If enough people are willing to talk to you, you'll figure out some way of dealing with the money issue.