Well, balance in cata is a pretty squishy class, but not the squishiest whatsoever. Duel a lot and play wsg and you'll get better and know how to face different classes. I'll list what to do against most common classes:
Rogue - You'll probably get opened on so it'll be tough if the rogue knows what he's doing. Throw a rejuvenation on yourself ASAP, use lifeblood/warstomp if you think you absolutely need it, because balance vs rogue is not always easy. Try to fakecast and throw a few regrowths if possible, but not if you're already on very low hp obviously. Distance is easily gained with travelform but as soon as he pops sprint, you know it's gonna be tough. Get demo roar on the rogue, make sure rejuvenation is ticking on you and moonfire is ticking on the rog the whole time. Use thorns if you think he's gonna get a lot of ToT on you. When you have enough distance or have juked his kick, root him (or starsurge if you know you wont get gouged either). At this point, if the rogue has no sprint or shadowstep left, you should have a big chance of winning the match as moonfire + thorns have already done a ton of damage on the rogue. If you wanna play safe, just camp travelform and moonfire spam the rogue and keep rejuv rolling. If you happen to find a rogue and he cant open you, the match should be yours. Wanna play safe = camp travel & spam moonfire.
Hunter - Same as rogue, if he opens on you and knows what he's doing, it's gonna be tough. If not, try to get something to hide in, for example behind a stump in mid or simply at a direction the hunter isn't looking atm. Start with starsurge + starfire and moonfire and the hunter has lost a significant amount of hp already. Now just keep yourself alive, you can try to avoid a bit of that burst by using LoS and casting a few regrowths + rejuv. Keep moonfire rolling and keep alive and the match is pretty much yours. Cast a few cast-time spells if you think you can without being blown up.
Warrior - Should be very easy for a good balance, if you know how to get out of piercing howl which might take a little bit of practice. But once youre out of range of piercing, keep him in combat so he cant charge, keep rejuvenation on yourself or heal if youre at critical amount of hp, then it goes exactly like against rogue: Cast a few cast-time spells or travelform + moonfire. Not hard. The troubles only start if you can't get out of piercing howl, since fury does some sick dps in cata as you might know.
Mage - Frost shouldn't be a problem, heal when necessary and dps when you can. Fakecast his CS and you have a win already. Arcane is a bit more tricky because of stronger dps + improved cs, so try to find a place to LoS with if things get tough. Faking CS is crucial or you will lose 1v1 very easily. Keep at decent amount of hp before he has cast CS, because that 4sec is a long time against a class throwing 500 instant cast spell crits ;P But yeah, just heal yourself, keep rejuv + moonfire up if possible, cast when you can, and heal when you feel like you're at vulnerable amount of hp (I'd say 700ish is quite low against an arcane already since barrage + fireblast are already 700dmg if both crit). Btw, don't panic if he interrupts your starfire/starsurge, you can still cast healing spells and wrath
Priest - This match you won't win 99% of the time, if the priest knows what he's doing. Maybe if you happen to crit with starsurge + starfire in a row and he's not paying attention, you might get a lucky kill. But don't get in 1v1 with a priest, you won't win.
Paladin - Might win 1v1 if you're good, but hpala has the advantage again with powerful heals and the ability to HoJ + exospam you. Generally don't try to nuke a hpala down 1v1, it will be hard as fuck and if he has anything to LoS you with, it simply won't happen. Retris are a bit different, but a very hard 1v1 opponent aswell. Keep your distance to not get 1-banged by TV and to not get in HoJ, and try to keep him under pressure with dps. Chances are you wont drop him if he knows when to heal but #1 priority is to not let him close to you. If he gets you in HoJ, you're dead 90% of the time.
Shammy - Shouldn't be a problem winning 1v1, just keep your HP and fakecast those wind shears. Enhas do quite a bit of burst so be aware of that, too.
Locks - Same as shammy, but their damage is very different with the dots + drain life. You will have to keep rejuv up at all times and cast a few regrowths so you dont get killed whle trying to nuke him, but generally if you dont get surprised by dot dmg, you should win a lock with very simple actions, IE healing, and dpsing when you have enough hp to safely dps him.
Now these were only for 1v1 combat, now some general advice for a druid / boomkin:
- In a normal wsg running with your team, don't get in the centre of attention, but try to attack by surprise and cast from places that enemies wont see you easily so you get a few free casts on the target before he even notices what's happening.
- Learn to use your travel form and all other abilities as effective as possible. Roots are a very good CC if you know when to cast it and to who. When dueling vs non-stealthers, go in prowl before the duels starts so you can open the fight whenever you want and with a little surprise.
- Don't be a tunnelvisioned "LOL I CRIT 30% OF THE TIME IM COOL" boomkin and spam starfire 24/7 hoping to get KBs. You have effective healing with rejuvenation and regrowth, and roots to keep enemies from escaping / getting to kill your friends. Moonkin in the 19s can often be considered as an offheal / support spec, which it definitely is very efficient in. It's not your responsibility to keep your teammates alive in offence generally, but when a healer is missing or you see you can save someone by casting a few regrowths, for gods sake, do it.
- Get an FC set and be always ready to FC as you will be required to FC at some point or another, and that's a fact. Balance FCing is a bit different from resto and also a bit harder aswell, as you can't mobile heal with swiftmend and your heals are weaker, along with lower hp in bear. But keep in mind you also have more dps to dispatch enemy offence, and starsurge is a perfect spell for this. You will probably need a good healer with you too, since balance fcing as solo (and solo fcing generally) is something very hard.
Not much else comes to my mind right now, if you need any more advice, please let me know
Happy twinkin with ya boomkin!
Also, best druid guide out there:
http://www.twinkinfo.com/f12/19-druid-guide-6715/