A lot of forums have specific threads designated for welcoming new members, where those who have just registered are encouraged to introduce themselves. Your introductory post should basically inform the other members who you are and why youve joined the forum. The reason you give should not be in any way business-oriented. Making a sales-pitch in your first post will definitely be frowned on and may get you banned.
Do not post immediately. Most forums have at least one, large, close-knit community in it. If you suddenly post on a thread where discussions have been carried on for days, you shall be shunned and ignored. Spend some time going through the archives?figure out which topics are perennial favorites and which users are the unofficial leaders. Also observe the particular etiquette of the forum.
Whenever there are questions asked that fall within your area of expertise, answer them to the best of your ability. Back up your answers by providing links to trusted sources and answer follow-up questions promptly. If you prove to be a helpful, efficient member, youre more likely to be paid attention to.
Do not get involved in heated arguments, no matter what you think of the question at hand. Keep reminding yourself that youre there to build up a clientele for your business; stay away from topics like religion, race and politics; dont immediately respond to criticism; make sure the others know when youre joking; leave discussions when they become contentious.
Once youre acknowledged as a respected user, start marketing your products aggressively. Focus on techniques which are likely to prove beneficial to the community as a whole