The most important thing as a new community member in any of those sites and our forum, make sure to read the rules and know who are you dealing with. The best exchanges are done with people whom you communicate with and developed a sort of friendship online. For instance @dantzig is my best online friend, awwww I would gladly send him a kidney if he needed one.
Many of these sites require newbies with zero feedback to send out first. Read the feedback from a member you're dealing with and ta-da, that's pretty much everything. I'm sure some other guide will post some best practices.
Our forum is made for passionate people who collect stickers and trading cards. Why just browse, when you can register for free and get access to all the functions. Start discussing and swapping with collectors around the world?