I've done the rogue/shaman duo 3 times. Ranger will be fine.
Depending on gear/mana, either one can root until it's slowed. The ranger should tank to let the shaman med.
Also, in addition to using inner fire to heal (until 19) you will also want to play with your root and slows. The level 1/5 roots will suffice for holding the pull/adds until slowed. The extra mana isn't worth the extra slow percentage until later levels. Use a slow that is "good enough" so you can handle slowing every mob and deal with resists. If you're struggling with mana and only slow certain mobs you'll spend that mana you "saved" on heals anyways. If the ranger is taking "too much" damage or you're keeping up on mana, go up one level of slows.
I'd also recommend using something for buff timers. Not having to swap spells mid-fight or holding pulls to refresh a buff adds up. Being on top of buffs makes a notable difference.
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