1. Mirror image is usually used on boss fights, or when you need slightly higher dps on trash. I'm unsure of the glyph, but the page at EJ will tell you the most recommended glyphs for you to get. Use it when it will not pull other groups, and when it will be ready again for boss.
2. Always use Flame Orb on single target fights. It's a 1 min CD for mages, for fire mages it gets even stronger. While handy for trash, sometimes it will move beyond the group you're working on and explode/start casting on other mobs, so only use if you know it will not pull more. It will end up doing roughly the same damage as a fireball crit. Plus it can also crit, adding to your ignite debuff.
3. Start out with Blast Wave, it's way less expensive than flamestrike, and it will automatically apply a flamestrike if there are 2 or more targets in the blast radius (if you have it talented). I then use Living bomb, and scorch the target till Impact procs and I then spread it to all nearby mobs. Reapply blast wave whenever it's off CD, with flamestrikes in between when blast wave is on CD.
Dragon's Breath doesnt do a whole lot of damage, but can be useful when interrupting a mob if your counterspell is on CD, or if the tank is taking a lot of damage by incapacitating the mobs for a tiny amount of time before broken. You generally shouldn't use this unless you need to get the adds off of you if you pull off the tank.
Basically, the EJ guide is where you'll wanna go for more information. It can be a little difficult to read at some points (when it gets technical) but it contains all the information you need. I know you say you've read it, but your questions are all answered in there.