Equity

You can really clean up with a small, rapidly growing company, if they offer equity (a piece of their action) as part of the compensation package. You will give up some salary (perhaps up to 10%) to get an equity position. The clues you need to understand thoroughly, in order to do this successfully, are roughly:

1. They have a tightly focused, unique business idea that can be explained in no more than two brief sentences and is fairly obvious.  You read those sentences and feel is it a great business idea (as in, why didn't I think of that?!).  
2. Key component here is no significant competition.  If they already have competition, you're probably too late to clean up.
3. You can get access to, and can read and understand, their tax and accounting filings.  You'll have to do your own homework there, but looking at their financials for the last 4 quarters prior to your hiring is very important, especially if you learn to read between the lines.  
4. The company should be showing roughly exponential growth in sales, revenue and profits for the year before you hire.  This point is most important for employees with an equity component to their compensation package.  Pure employees (no equity) need this less.
5. Their market must be very large compared to their ability to service it: room for growth.
6. During your interview, you had the opportunity to talk with the entire management chain, including the CEO.  You need to leave with a good feeling about all of them.  
7. Make sure you ask about how they conduct sales and the sales climate for their product or services.  They basically need to tell you the equivalent of: "Sales for us are easy because we make them an offer they can't refuse."  Be nice, but make them show you it is true.  It is a reasonable request from a prospective employee taking an equity position in lieu of some salary.
8. Let's pretend they offer you 5000 options for stock as part of your compensation package.  Can you calculate the current value of those options? You have to do it independently of folks from the company, because they are motivated to get your hard work, and may not be showing you the whole story.  Long story short: If those options have negative value (company is in net debt, options are upside down), you should leave it on the table: refuse the options and just go for pure employee compensation (if the company is otherwise worth working for - totally different question).  Options must have present net value equal to or greater than the salary they are asking you to give up.  Would you invest in the company if you were not going to work for them?
9. Do they have reviews on Glass Door? Read every one of them.  Have they been sued? Check the court records.  Are there any sexual harassment claims against them?  Are there any other cases pending, or judgements against them from the past?
10. How to they measure up against similar companies (same amount of time in business, same size, similar market niches)?  Are they leaders, somewhere in the middle of the pack, or trailing (losers)?  Guess which category you want to give up income to be a part of ...
11. When you go to the interview, you need to be as prepared as a lawyer going to trial.  You will get exactly one shot most of the time.  Thoroughly school yourself in the psychology of intimidation (as in, read Robert Ringer's Winning through Intimidation). You need to be relaxed, comfortable, on the top of your game, curious about but not needing the job, and able to rapidly scan the folks working at their cubes when you go to the interview.  What is their body language communicating to you? Are they glad to have their jobs, or scared, sullen, what?  That feeling you get will tell you more than all the actual interviews combined about the character of the company and its leaders.

This post probably isn't all inclusive, but it gives you a flavor of the large amount of research you need to do before taking any job.  Jobs with an equity component require an order of magnitude more research than straight employee jobs.  As always, your best bet is to secure as many options at the same time as you can line up.  It takes a lot of work, but that effort is the only way you will win consistently at the employment game.  Good luck!