If you want to gain entry to any industry there are certain obvious things you need to learn -- a body of knowledge about technology or law, for example, formal procedures, the identity of the sector's key players, etc. These things are usually written down and accessible to anyone with the will to study them.

But there are also unwritten rules and unconscious mores -- what to wear, which jargon will make you sound like an insider, cultural norms. Unless they have a seasoned guide to help them, newcomers generally learn this sort of stuff by sometimes embarrassing and costly trial and error.

And despite its much proclaimed openness to talent and belief in meritocracy, that applies to Silicon Valley too. Just as with any other industry, Startup Land has its own unspoken etiquette that can make moving into the industry initially a little forbidding to those who didn't come up surrounded by tech culture.

Thankfully though, those who have managed to make the leap from bumbling newbie to Silicon Valley veteran occasionally reach back and offer a helping hand to those coming up behind them, posting their hard won understanding of the Silicon Valley manners and mores. Here are a few of the most essential rules.

1. You must answer email immediately.

You can find a million articles about finding a less life-consuming and more psychologically healthy relationship with your email, but if you want to fit in among the Silicon Valley elite those articles don't apply to you.

"You have few hours to answer the emails you receive. Same day is the norm. Next day is acceptable. Anything beyond 24 hours could be a problem," claims Frenchman-turned-Silicon-Valley-exec Roman Serman on Medium. (He even confesses to being so clueless as to have actually worn a tie to his first meeting at Google in the post. "It took the Googlers a full minute to realize that I was not a limo driver," he recalls.)

2. Introductions demand a double opt in.

Everyone likes meeting new, cool contacts, and that's as true in Silicon Valley as it is elsewhere, but no one enjoys being surprised by a connection they didn't agree to. Here's the accepted procedure if John wants to introduce Paul to Helena, according to Serman: "First, John asks Paul if he agrees to being introduced to Helena. Then, John asks Helena if she is OK to be introduced to Paul. If both agree, John makes the introduction."

3. Emails should be no longer than five lines.

Wait, you object, what if I have something really important or complicated to explain? Too bad, replies Serman. The ability to squeeze information into a succinct and compelling package is highly valued in the Valley. "Your communication must be succinct (3 points, 5 lines max), crystal-clear (no PhD in philosophy required to understand you), and precise (data, data, data)," he insists.

Serman points readers to a post by Y Combinator partner Michael Seibel on How to Email Early Stage Investors for more details on the exact format favored by industry bigwigs.

4. The right time to tell you story is all the time.

"Every email, conversation, or message of any kind is an opportunity to sell your company--subtle or not. Give people a link back to your company in both your signature and email address every single time," advises Minnesota-to-Silicon Valley transplant Michael Pollock. "You have to be in a sales-mode. All. The. Time. Night and day," agrees Serman.

5. Ask for the shortest meeting you can.

Maybe because of all the email they're processing all the time, people in Startup Land are busy. Really busy. So forget the one-hour meetings that are standard in much of the rest of the business world. "I often suggest a quick 15-minute call to talk about X, Y, Z specific points in order to not waste someone's time that doesn't know me yet," notes Pollock.

Serman says much the same thing: "If things and decisions can be wrapped up in 30 mn, why should you request?--?and block-- a one-hour slot in the other person's agenda? If you request a '30 mn meeting', you show that you presumably know how the system works."

Silicon Valley veterans, would you add any other etiquette rules to this list?