There are a few things that can help your battery last longer before needing charged again. One way is to disable things such as GPS that require the phone to run background tasks to keep the location and other things updated. Also programs like Facebook, email apps, and others that also run background tasks to sync information and keep things current and up-to-date will cause your battery to drain quicker. So by changing these apps settings to where they are not constantly trying to update themselves will definitely help some. If you have already done this and it has not helped it may be time to replace the battery.
Lithium ion batteries will also hold a charge longer and have a longer battery life if they are used with the correct charging equipment and chargeed properly. when charging a lithium ion battery you do not really want to leave it on the charger for long periods of time. These batteries actually last longer if you plug them into a charger at about 10 to 20 percent battery life and let them charge to about 90 percent and then remove it from the charger. Overcharging and also letting the battery discharge too much will affect its battery life. So if you do replace the battery make sure you are using the correct charger and try not to over charge the battery or let it completely die often. I know sometimes this can't be avoided but the more one does avoid leaving it on the charger or letting the battery die the longer the battery will last. Although even when charged and taken care of properly these batteries just never seem to last as long as one would hope, especially if they are used often.