You got great replies from the main people here. The only thing I will add is to pay attention to the rules and the post based account restrictions. Posting something generic, like "following", may be seen as an attempt to inflate your post count, which is frowned upon and can get you in trouble.
Commenting on a post will automatically follow the post for you, however if you wish to follow without commenting (or as I do unfollow posts as they age), then there is a link right above the "#1" of the first message in the thread that says "Watch Thread" (or if you're already subscribed, it'll say "Unwatch Thread"). This will allow you to get notifications and optionally email messages for new posts in the thread.