In the real world, this usually amounts to how you dress, how you style your hair, how polished your shoes are, etc.
There are certain civilities that are usually followed on online dating sites that you would be wise to uphold (this mostly applies to guys, but girls can be guilty of them, too).
Firstly, don’t be that creepy guy who sends awkwardly sexual messages to girls half your age, writes intentionally offensive things in the forums or harasses other members.
This also means that you should keep yourself open to dating different types of people.
I have a very definite type that I tend to gravitate toward, but I’ve found that when I’ve dated people who are very much outside of that type, I’ve been just as happy or happier even though they wouldn’t have fit my usual description of what I look for in a woman.
If you’ve been back to the same person’s page 10 times today, it’s time to send him/her a message, otherwise you might become known as a ‘lurker,’ essentially the Peeping Tom of the online dating world, who is basically there to look at other people’s profiles and do god-knows-what while looking at them. Thirdly, if someone sends a message to you, it’s usually good form to send them something back.
Now, if their message to you is at all off-putting (sexually-charged, offensive, too short to glean anything from, etc), then just delete it and go on with your day.
It’s simply not cool, gives online dating a bad name, and will likely get you reported and booted from the site.
Secondly, most sites allow some kind of opt-in or opt-out functionality that allows people to see who has been viewing their profile.
Put yourself in the shoes of someone who is visiting your profile.
Say you want to come across as sweet, but with a sexy side. If not, balance your photos a bit better (have some that show you being sweet, some that show you being sexy, with the balance being about what your personal sweet:sexy ratio is), insert a few more salacious comments among the cute ones, and check it out again.
Typing is fairly easy for people of our generation, and it doesn’t take much extra effort to look for typos (most modern browsers will underline incorrectly-spelled words automatically, and offer to change it to the correct spelling if you right-click the word), make sure that your message makes sense and change the ‘4’s to ‘for’s, ‘2’s to ‘too’s, etc. Who in their right mind honestly believes that this porno-inspired pick-up line will work?