Whenever I'm on my archer I usually check the leader box and get it due to high gearscore/rating. Whenever you are calling out instructions, always use /n to get peoples attention. Many people don't read raid chat so typing there is next to useless. Use clear and concise instructions and repeat the most important parts. I usually go with a wall zerg strat unless I see some recognizable good pvper on the other team. Refer to specific people or classes when assigning roles. "Warriors and lancers attack cannons in mid," or "such-and-such archer and X zerker stay and defend inner ladders, Y warrior get in inner cannon and call out airships."
Hit M and use the button in the top left of the map to scan, especially while defending. I usually stay inner ladder on defense so I can scan on cooldown. And yeah, don't get in a tank while leading because it bugs out scanning sometimes.
All in all, if you get stuck in the leader role embrace the opportunity and be confident in your instructions, and hope that your teammates speak english lol.