When is the best time to start advertising for your forum?
I am currently trying to add at least one topic for every forum and asking open questions to persuade members to start posting more. But the issue is out of the few members I have, only one really posts now and then. I need more members, and I need to get the word out, but is there anything else I should do beforehand?
To be technically correct, you have already started to advertise, ie. placed that link in your post.
Anyway, look at it from the user's perspective. Why would they stay on your forum if say you had no topics to post in (etc.)? Be sure your forum also appears active; you could ask someone to help you out.
Post lots with that one member! Long as they are having fun then you got something. You should make the most of that interaction. Show everyone else who visits what fun you're having ^_^
Seeing others having fun on a forum is what entices more people to join.