3) Turn off data roaming
If you live anywhere near a border, or do a good deal of traveling, you'll appreciate this when you don't get a Christmas-sized data bill out of the blue. Get into Settings, choose the More option under Wireless & Networks, then choose "Mobile Networks," and un-check "Data roaming" in this section. It might already be un-checked, but if it's not, you just did a great thing. You can easily turn it on again if you really want to use another country's dollars-per-megabyte networks—you'll get a prompt.
4) Add your spouse, kids, parents, or other important contacts to your home screen
You'll click the phone dialer, messaging app, and your email shortcut many, many times getting to that one person that you talk to all the time. Unless you tap on that center button that holds all your apps, scroll over to the Widgets section, press and hold on the Contact option (if there are two, it is usually the second pick, with the smaller 1x1 size), and drag that Contact onto your home screen. You'll next pick the contact you want to give this prime spot, and now whenever you tap their icon, you can quickly message, call, email, or even get navigation directions to their home, if you've filled out their contact entry.
5) Create a shortcut link for directions to home & work
About half the time you're getting directions in unfamiliar places, you're leaving that place for a common spot: home, work, or a close friend's home. It takes some time to load up Maps, enter the same old address while Maps furtively attempts to auto-complete, and confirm that, yes, you want to get out of here. Here's the shortcut, similar to the contact trick just above: head to your list of apps from the bottom-center screen button, scroll over to the Widgets section, and look for the Directions & Navigation widget. Drag it up to your home screen, and you'll then be prompted to give it a name ("Home," "Boyfriend," etc.), choose whether it activates just directions or spoken turn-by-turn navigation, enter the address, choose the method (car, bike, walk, public transit), and choose an icon for the shortcut (helpful if you're creating more than one).