I've been invited to a friend's LAN. I've never played AoE2 before. What are the absolute basics I need to know? What are some rookie mistakes I should avoid?

I hope this question isn't too broad to answer.

I'm no stranger to RTS games in general, but have never played AoE. I don't think any of my friends at the LAN are exceptionally good at this game, but they've all played AoE for some time.

What do I have to do to not get absolutely destroyed? I have three days to get ready, so I'm thankful for any advice.