You're right, nobody really knows. It changes for everyone, and over time. People at age 50 are not seeking what they were at age 22. But to be successful on line, you will need to get replies to your 'ice breaking' emails and instant-messaging. Here are a few suggestions to increase the number of replies you'll get:
• Take your time, and think carefully about how you compose your Internet dating profile. Check for spelling mistakes, and for gross grammar errors. These are important rules to follow.
• A succinct description is best – you won't lose their attention. Keep it short and honest. Being truthful now will prevent potentially serious problems later.
• Unless you're just always a serious person, be sure to stir a pinch of humor into your profile. Keep it fun. Humor is a great icebreaker. Don't be too serious at first.
• You really need to clearly express the type of person who you wish to meet, and why. This is the best way to sort the wheat form the dating chaff. Customarily, adults will have a good idea of the kind of person they're attracted to. Though most are not clear as to why.
• Be sure to write the thing you like, including music, movies, books, and anything else that occurs to you. Also, if there's something you simply can't tolerate in a person, get that down too. And be courteous when you describe something you don't like in a person.
• Statistically, the most important thing you can do to get replies or inquiries is to post a good, clear, recent photograph of yourself to your profile. If you can, post more than one. People with pictures posted get many TIMES the number of interactions as do those without photographs.

• Instant messaging seems to have a very small following in the Internet dating scene. If you do opt to IM, as it's called, be polite. And don't hit 'send' and then immediately start being worried and getting judgmental about the length of time it takes to get a reply. That person no doubt wants to check out your profile before they decide whether or not to answer you. And remember your message will just 'jump out' in front of them – no matter what they are involved in. It's kind of invasive, so handle it accordingly.
• If someone doesn't respond to you, don't make the mistake of blocking them. There are any number of reasons they didn't respond. Maybe they were just too shy. Give them time – as long as they want. Meantime, you continue your search.
• The first email should be succinct, interesting, and lightly informative. Humor is always good! Don't be too funny just yet, but keep it relaxed. You don't want to include too much detail just yet. Be sure to mention any of the things that you have in common. Try to be 'conversational' in your writing – not stodgy or too formal.
• Think probabilities! Contact several people at the same time. Don't just send out a form letter either. A form body is okay, but be sure to fully personalize it. Nobody likes that assembly line thing. Select a few people who you have matched well, not those who you have nothing in common with.
• Honesty is most assuredly the best policy in the Internet dating game. Be honest. As numerous bits of humor in virtually every media have suggested, in the ethereal world of the Internet, it's all too easy to change, subtract, or add things that cannot currently be verified. But what goes around…
• You won't like it if you don't get a response at all, and you'll prefer getting one quickly, even if it's a polite "no thank you." So be considerate and always reply quickly to any messages you receive.
• The prudent (and successful) Internet dater doesn't bring up money, power, sex, or possessions at this early stage. It should be assumed that both parties are seeking a person, not some possession(s), position, or savings account balance.