Quote:
Maybe I couldn't click their portrait fast enough to select them so I could heal them.
Don't do it that way. Get yourself "Clique" which is a fantastic addon that'll make your life much easier. It allows you to assign spells and abilities to mouse+keystroke combos that you can then just use by hovering over the target that you want to heal and pressing/clicking whatever spell you want to use. This works exceptionally well with shamans since their ******* of heals is fairly limited.
For example, I have things set up so
Shift + Left Click = Lesser Healing Wave
Shift + Right Click = Chain Heal
Shift + Middle Click = Riptide
which is just about everything I ever need, with the rest being bound to Alt+Clicks. It doesn't get any faster or more convenient than that. To set things up, you just install the addon, which adds a tab to your spellbook, and then just perform your desired click/key combo while hovering over the ability in the spellbook.
Don't worry about gear while you're still in Azeroth. Most of it is fairly useless. Generally you want anything that has Intellect on it, with Spellpower not really being available until you're in the mid 50s or so. There will be a bunch of cloth items you can pick up at 30+ if you're running Scarlet Monastery, and you'll get more if you continue running those random dungeons.
Once in Outland, the very first quests will give you what you need. Don't waste gold for gear at the AH.
Most importantly: Accept those random groups for what they are. No matter what really happened, its always the tank's or healer's fault if things go wrong.