It has improved considerably since the first time I noticed this phenomenon back before BC, but I still see this now and again: people who don't focus their gear towards their immediate goal. If you were to inspect every Pally you saw for the next week, I'd guarantee at least 10-15% have gear for multiple roles on at the same time: healing piece, defense piece, str/crit piece.
Nothing weakens your ability to handle your current role than wearing something that doesn't fit. For every piece of gear that has int, +heal and mp5 on it you're losing that much in item value of strength, crit and stamina, or vice versa.
This can be said for Prot Pallies and Holy Pallies too, but we're over here at Retnoob, so I'm going to speak to that gear.
I've mentioned gearing priorities before but I'll lay them out in more detail now.
First, no healing pieces, no pieces with defense or block/parry/dodge rating. Period. Don't even TRY it. If you're healing/tanking for a fight, then swap to the necessary gear set. Oh, and carry multiple sets any time you're raiding. If your raid needs more healing, be ready to help out. No, you're not great at it, but you're good enough, and that's what counts. Carrying multiple sets for 5-mans is nice too, but I've suffered bag space problems enough to understand anyone who chooses not to.
While you're DPSing though, your gear should consist ONLY of the following possible stats: Strength, Agility, Stamina, Intellect, Crit Rating, Attack Power, Hit Rating, Spell Damage and the occasional touch up of MP5 if you're wearing a mail piece (which is acceptable while dpsing/healing, and offers a huge array of useful gear for you). Spell Damage is NOT a priority, you just get it on the occasional piece and that's fine. Until I started picking up S2, I had a grand total of 5 spell damage, from the set bonus on my Warmaul of Infused Light, and I never had a problem with it.
If you maximize the potential of your gear, it will go a long way towards improving your damage. If you continue to wear whatever you have, everything is diluted and you can do nothing well.
Now, let's talk stats to shoot for. This is a common theme:
Attack Power: 1500
Crit %: 25
Hit %: 9
9% to hit is what you need to eliminate misses on boss mobs. While Sword/Mace spec used to get you a LONG way to that goal, it will now only offer 1% to crit, so forget about it. You need 9% to hit with talents, so 6% after you pick up Precision from the prot tree. The hit rating required from gear for 6% is around 96, which isn't too hard to get once you start gearing up in Kara (again, wear mail gear. Plate DPS gear is nonexistent until Nightbane).
Crit Rating is important for two reasons. One reason is Vengeance, because Vengeance is great and wonderful and the reason for our existence. Every crit keeps that 15% increase to your damage up. It will be less important in 2.3 when Vengeance lasts for 30 seconds. An abomynal crit % would be required to not be able to keep Vengeance up at that point, something akin to 15%.
Reason Two is just as important. Everything we do CRITS. SoC, Melee, JoC, CS, etc. Thus a 25% crit rate increases our DPS by 25%.
So you keep a solid amount of Crit going, but never so much that you're not pimping out on the AP. AP is ultimately the most fundamental DPS stat. If you have a 35% crit rate but roll with 1200 AP, your crits will look like my hits at 1600 AP. That's why 1500 is the stat to shoot for. It's not gonna be easy, or perhaps even possible, without some raiding/arena gear, but it's your first milestone. From there you push on to the higher numbers, but 1500 AP, 25 Crit and 9 Hit Rating is when your damage starts to become truly noticable.