1)
Search first. If someone has already posted a similar thread, it saves your time waiting for a response to a new thread.
2)
Use a descriptive title. It helps other users find answers to questions that might have already been answered before.
3)
How old is the thread? If you're going to post in a thread that is more than 6 months old, create a new thread instead. If you do post in an old thread, you will get an infraction, and possibly be temporarily suspended from posting.
4)
Encase your code properly. It makes it extremely hard for someone to debug your code if there is no syntax highlighting. Syntax highlighting might also bring to light any typos you might have made.
Examples:
[php]echo 'Sample';[/php]
[html]<p>Sample</p>[/html]
[code]body{ background: #FF0; }[/code]
Code:
body{ background: #FF0; }
5)
Be polite. If you're polite when someone helps you out, it will be likely they'll be more than willing help you next time.
6)
Give thanks! If someone has helped you out, click the scales icon (

) next to their post and choose to approve their post. This helps to show who's really nice!