Location Services: The ability for your iOS device to tell apps where you are is one of the greatest things about iOS 5, but if it's killing your battery, it's not nearly as helpful as it could be. You can switch location services off entirely by going to Settings -> Location Services and flicking the Location Services Switch to the Off position. But that's an extreme action and one you can likely avoid. Instead, scan down the list of apps and take a gander at which of your apps are currently using those services (as denoted by a purple arrow). Do you really need those apps broadcasting your location? If not, switch them off.
With regard to locations, one app to keep a careful eye on is Reminders. You can have reminders appear when you're near a particular location. This means that your device is routinely performing "Am I there yet?" operations, which affect your battery. It's a very cool feature, but if your device can't hold a charge, it's a feature you may want to do without.
Siri: If you've got an iPhone 4S--remember, Siri is only available on that phone--go to Settings -> General -> Siri and disable the Raise to Speak option. This is a convenient feature that invokes Siri whenever you lift the phone to your face, but I've seen reports that this can cause an undue battery drain. With this option off, all you have to do to awaken Siri is press and hold the Home button.
I'd resist disabling Siri altogether. When you do, the information Siri has gleaned from you is wiped from Apple's servers. When you switch it back on, Siri is not terribly responsive out of the gate, plus it then resyncs that data with the cloud, thus burning up power.
Push: It's always been true that when you push data to your iOS device, you'll put more strain on the battery. To preserve your battery charge, turn push off by going to Settings -> Mail, Contacts, Calendar -> Fetch New Data and flip the Push switch off. Your device will now fetch data with a setting of your choosing--every 15 minutes, every 30 minutes, every hour, or manually. Choosing Manually saves the most power as data will be delivered to your device only when you use an app that requests it--when you open Mail, for example.
You can also pick and choose which accounts push (if supported) and fetch. To do that, scroll to the bottom of the Fetch New Data screen and tap Advanced. You'll find that you can adjust settings for each account you use--iCloud, Gmail, and Yahoo, for example.