Either they aren't trying or they fail at life. Being unaware of the mechanics on some fights is sometimes a reason but typically if it's important then the raid will tell you, like standing in dead sparks on malygos or in the blue circles on iron council.

Gear isn't a major issue. Once you're at least in 200 blues, aside from a few pieces(usually weapons or trinkets) you aren't going to see a big dps increase items. A full tier upgrade is going to help but a couple pieces isn't.

Unless you have some really retarded spec, it isn't going to be a big issue either. As long as you have all of the key talents the rest won't matter much.

Rotation doesn't matter all that much. As long as you're using the spells you should be using(and only the spells you should be using mr. arcane barraging frost mage) getting them all lined up perfectly isn't going to make a big difference. Castrandom with a hunter isn't ideal, but it isn't far off from what a real rotation is going to do. A frost mage doing straight frostbolt spam and using cooldowns whenever they're available isn't going to be far behind once that's timing cooldowns properly and using ice lance during fingers or frost procs.

Glyphs sometimes matter. Flame shock is very important for elemental shamans, but after that the difference between all of the other reasonable glyphs isn't so great.

Just mash whatever skills/spells you speced for and you'll do passable dps. Do them in some reasonable order and you'll do decent dps(like an ele shaman doing flame shock then lava burst). As a general rule, at least for casters, it's not worth it to stop casting to wait for a powerful cooldown, IE if lava burst is .5 seconds away from being usable, cast another lightning bolt or chain lightning instead of waiting for it.

So basically just tell them what spells/skills to use, a rough order to do them in, never stop attacking unless you need to get out of the fire, and to mash instead of waiting since it'll help minimize lag downtime. It won't be the best dps but it should get at least decent.