Easiest thing in the world mate. A worthwhile post is practically anything deemed not to be crap and a post clock. Can be on any subject such as something funny that's happened to you, a list of your hobbies or even what you had for dinner last night.
What newbies tend to miss is that a like is also required. This too is easy and newbies often get them for showing they've put a little effort into their post. Newbies are given an excellent chance to get off to a good start with the "who are you?" section. Most simply post hello or hi. Those who actually answer the question, who are you? with a well worded introduction are often rewarded with a like or 2.