As we get to know, a Balance Druid is a fun build. "A Mage with Plate Armor" and that's exactly what it is. Consider this, if you build a Druid when you get bear form you get a 400% armor boost. This enables the bear to tank for a 5, 10 or 25 group as well as solo. At level 40 a Druid that has run the Balance tree gets Moonkin Form. Moonkin is a highly armored form that allows you to cast nature spells. So you have high armor and severely high spell damage.
   Above all, I would like to say this, if you get accepted to a serious raiding guild with this highly controversial spec you should consider yourself lucky. It's just a fact that most endgame raiding guilds only accept one Balance Druid, if even that. You have a far better chance getting into a guild if you are Resto or Feral. I asked my old riverdance partner Kuur what his suggestion would be to people who are interested in speccing Balance, his answer was: "Don't do it!". We didn't elaborate much deeper to why he chose those words, but I kinda understood what he meant.
   Let's talk about what your role in a raid will be. To cut it short, you are there to buff the 4 other casters in your group with 5% crit aura, combat resurrect the noobs that died too early and sometimes you might even be asked to save your innervate for a healer (be sure to have a "No habla Ingles" macro ready for those occasions, if that fails just put them on ignore). You are not in the raid to top DPS meters, well you might once in a while on trash or even score high on a Boss fight. But you will most probably never be in league with Warlocks and Rogues for example, so get used to that. The only way I can see that happening is if you are the actual Guild Master and decide to take all the best loot before any other class. This I tell you so you are prepared and don't fall apart after 3 months of raiding and never being nr. 1 on DPS meters. Ofc there are Moonkins with exceptional gear and skill who can top their guilds DPS meter, even I have occasionally done good and received a cookie. But don't get your hopes too high.
   In comparison with your gear, your Spellrotation can make a difference. And it's not just the gear in it self but in most case the gear you are wearing will tell where you and your guild is in PvE Progress. Now of course this can be opened for discussion but if you are wearing T4 (or equivelent) you and your Guild are probably doing Karazhan, Gruul, Magtheridon and perhaps Zul'Aman. If you are in T5 (or equivelent) you and your guild are probably doing Serpentshrine Cavern and Tempest Keep. And finally, if you are wearing T6 you're probably a no-lifer. Starfire is the main ability I use in my rotation at all time, but I didn't always used to.
Here you don't get anything but Mana back from your set bonuses, so just go mad. The instances you most probably are doing don't have trash packs that takes ages and the Boss encounters are generally short. So just go nuts, Moonfire spam, see how many times you can spam the wrath button between each Global Cooldown and then try to break that record. See how many Crowd Controls you can break before you get kicked from the raid, just go nuts. As long as you learn something from it.
Now things become slightly more serious. In most case, Wrath spam is the best spell for trash, unless you know the trash fights inside out. Most trash in Serpentshrine Caverns and Tempest Keep have annoying abilities to interrupt your 3 second Starfire, such as AoE Silence and AoE Knockbacks. Other annoying abilities are Spellreflection, Cloak of Shadows or retarded murlocs running all over the place and mobs that simply dies when you have 0.3 seconds left on your Starfire. When you take all this into account, Wrath spam is best in the beginning for trash. The Boss encounter on the other hand, they last quite long. You need to conserv as much mana as possible. Now I would recommend that you get 4 pieces of Tier 5 as fast as possible  and also aquire your very own from Badge vendor. If you keep updating your Moonfire every 10-12 seconds then not only will your Starfire do 10% more damage, but you will also have a chance to gain another 140 spelldamage for 10 seconds and if that Moonfire crits, your next Starfire will only take 2,5 seconds to cast. If mana really is a problem for you, just use Rank 1 Moonfire. Unless they changed it this wednesday, it should still work.
Although, it might be good to add that according to pure Theorycrafting, the following spellrotation gave highest possible DPS in a Mount Hyjal/ Black Temple raid enviroment.