Besides the references provided on this (and 100 similar threads), one can always resort to observing what type of posts are being merited, and derive a general idea from that observation (see https://bitcointalk.org/index.php?action=merit;stats=recent for example). The idea is not to copy anyone’s style, but rather to get a feeling of what is actually being merited on the forum, and from there, abstract an idea lead by example.