Ever read a book? </rhetorical question> Works just like the characters there. Go back to pages 1-2 on the story thread and see how the first post by any character went.
Your character arrives. Describe his appearance, his reactions. Include "interior" stuff (what he's feeling, thinking) only if you want- that's optional. End the post implying what his intentions are, where he's going in general and what he intends to do, and let the GM reply as to the result of those actions. Repeat.
He probably has questions on their arrival - maybe they seek out the Praeco's, maybe they wander over to whoever is nearby. Maybe it's light, maybe later near dusk. Whatever you think adds to the story.
Don't make any huge assumptions for NPC's without SG authorization- maybe the guards let you thru the front gate (safe bet, considering), but let Dierdre or Angus speak for themselves. HOWEVER, you can post something like "Assuming he catches up to the other magi, he then..."
If you're not sure, then post less rather than more- walk up to the front gate, and shout "hello", and see what happens. The key is to not run ahead of anything random that might happen, but not get bogged down in detail of every insignificant step along the way. Include things that show your character, that are fun for others to read, and that others would naturally notice (like Daggin's webbed fingers, that he sort of hides as a habit, but doesn't worry about with other magi), but you don't have to reveal "secrets" that are only between you and the SG (for now.)
Get started, don't be shy, you'll catch on soon enough.