Manage the number of open apps using the task switcher
You can double-tap the Home button to bring up the task switcher, then tap and hold an app's icon to terminate its process. Obvious targets to terminate are open sessions of most games (Angry Birds, Madden, NBA Jam, FIFA Soccer), Safari, etcetera.
The key point to remember is that iOS terminates apps in the background for you if it requires more resources such as memory. The rules that iOS uses are not clearly stated by Apple. However, from anecdotal experience and multiple posts online it is commonly believed that the apps that will be terminated first are the ones found at the far right of the task switcher, since those are the ones you have not been using recently.
What that in mind, terminating tasks in the first 1 to 8 icons from the left will most likely make a huge difference, since they will probably still be residing in memory. I see a noticeable difference whenever I terminate any of the first 1 to 8 apps in the task switcher--especially if they are games. Hope this helps.