Typing in all capital letters is the on-line equivalent of greeting acquaintances at a sophisticated cocktail party by howling like a hyena. If you don't want to be branded as a boor, an oaf, or a compu-nerd, brush up on your Netiquette.
Message boards are like small towns, with their own customs, ethos, and community standards.
Read messages until you get a sense of the style and flavor of a board, and the topics being discussed. Nothing is more painful to observe than the struggling newbie valiantly beginning a discussion of a topic that's just been chewed to rags. Learn the names of regulars so that when you begin posting you know who's who. Observe both the content and style of the posted messages and adapt your own contributions accordingly. So, once you've picked up a sense of place, leave a message about yourself.