In an ideal world, I’d respond to all the questions I get from people asking for advice. I like helping people; this is why I do what I do! In the real, time-limited world, I can only respond to about 25% of the questions I get from people. If your goal is to get a response from me, then you’re shooting to “outperform” 75% of people. Here’s how you can maximize your odds of getting a response from me and other experts.

#1: Use the Appropriate Method (Usually Email)

Most professionals have some system for managing their messages, and it usually revolves around email. Using a social network like Quora, LinkedIn, or Facebook disrupts this system.

The expert may never get notified about the message. They may have email notifications turned off or the email might be stuck in junk mail or filtered to another inbox.
The email might get grouped with other messages on this social network and accidentally archived / deleted.
The email subject isn’t indicative of the question. It’s usually just <New Message from _____>. Grr!
Most professionals separate their personal and work email. When you send a message to an expert through a social network, you’re sending a message about professional stuff to someone’s personal email account. Grr! This means that the expert isn't reading your message when they're doing work (and it just frustrates people who try to keep these accounts separate).
LinkedIn: I get a lot of LinkedIn requests from people I don’t know. The vast majority of them are just the default “____ wants to connect with you on LinkedIn.” You think I open up each request just to see if this random person I don’t know happened to include a message with their LinkedIn request? Nope. Never.
Facebook: Facebook filters a lot of messages from strangers into your “Other Messages” folder where you don’t get a notification of any kind. Most people don’t even know that this folder exists. Even if they do, they still probably rarely check it.
Quora: most of the messages I get on Quora should be Quora questions themselves. After all, you use Quora. You know that I use Quora. You’re asking me a question directly. Why isn’t this an actual Quora question which you can then invite me to answer?
Twitter: Twitter is actually fine – even great – if it’s a short enough question to be asked and responded to on Twitter. If It’s a long question though, use email.

Ultimately, if you’re hoping they receive your social network message because of an email notification, why aren’t you just using email in the first place?

“But I don’t have their email address!”

Did you try Googling it? My email address is widely available online (on my blog among other places), and yet I still get a ton of messages from people saying that they used a Facebook / Quora / LinkedIn message because they “couldn’t find my email address.” Oh really?

#2: Say Something Nice / Do Something Nice

While I don’t try to take a quid pro quo approach to helping people, the reality is that it works. I’m more likely to help someone who appears sincere, friendly, and helpful. I rarely if ever ignore a message from someone who has posted an Amazon / Flipkart review (assuming I know that they have). I just feel bad doing that. This person took a few minutes to post a kind review, and I can’t spend a few minutes helping them out?

Even saying something nice is a good start. It shows that you took the time to do a little research and aren’t just spamming a bunch of people with the same question. And, hey, it makes people like you more. People are more likely to help you if they like you.

#3: Don’t Ask If You Can Ask Me A Question

If you send me a message that only says "Can I ask you a question?" (and doesn’t include the question itself), I’m not going to respond. Just ask the question you want to ask. Otherwise, you’re wasting both of our times and distracting from other work I have to do. You’ll be in the 75% of people who don’t get a response.

#4: Ask Specific Questions

Emails like, “How do I prepare for a Google interview?” are unlikely to get much of a response from me. I could literally write a book on this; in fact, I did! If I respond, I’m just going to point you to my book. I’m not trying to be unhelpful, but it’s a very broad question and this is the most useful resource I can point you to.

#5: Ask Non-Obvious Questions

If you ask me a question like, “What does Google ask in Software Engineering interviews?”, I’m just going to point you to CareerCup (if I respond at all). Again, I’m not trying to be unhelpful here. This is the most useful thing I can give you.

#6: Keep it Short (200 – 300 words max)

Long emails not only take longer to read, but they are usually rambling and provide too much detail. When I read these emails (often those are just archived immediately), I often have trouble understanding what exactly the question is.

If you really struggle with understanding what is necessary information and what isn’t, then write a concise note and put the additional details in the bottom of the email (after your signature).

#7: Keep It Professional

Use good grammar and spelling. I’m not an unreasonable person. I don’t expect that non-native English speakers will suddenly be able to flawlessly speak perfect English. However, you can make an effort: write words fully (instead of using SMS abbreviations like “u”), punctuate a paragraph (mostly) correctly, etc. Here are some English tips that can very quickly and easily improve your grammar.
Don’t use obnoxious fonts (Comic Sans, etc).
Use paragraph breaks as appropriate. Long blocks of text are more difficult to read and understand. Sometimes, it's even hard to understand what the question is.
Don’t say anything inappropriate. Comments on a woman’s physical appearance is not okay in professional situations in the US. Ick. This is a surefire way to get me to not respond.

Again, I want to help you, but I can't help everyone who needs it. Following these tips will save me time and effort, thus increasing the chances that I respond to your message.

And, hey, if I do respond to you and it helps you out (gets you the interview you want, helps you negotiate, etc), let me know! Building positive relationships is always a good thing.