I have found that with my mixed group I have to approach each one individually and with the understanding that while doing dps with that toon I am just going to be spamming one button. On some toons, my hunter for instance, I use /click in a macro that triggers three other cast sequence macros. Pretty complex? Yes. Totally stolen from guys on this site. Yes. But it works very well. The concurrent /castsequence macros work well for my druid as well. As for my priest and warlock I have a single castsequence that works really well for them, atm. When that group hits 80 and I start adding haste and other stuff it may get trickier but at 70 I do really well.

As Ughmahedhurtz said, shaman are pretty easy. With my team 1 (pally x4 shaman) I can do every instance I have tried. Just be creative and read as much as you can about how others are doing what you are trying to do and don't be afraid to mix and match.