A lot of people who are new at this work their so hard just jailbreaking that once they do, they don't not what to do after that. Lets start off at square one. Most people jailbreaking 3.1.2 used Blackra1n, so you need to start by installing Cydia from the Blackra1n icon on your spingboard. Note: You need internet access to do this and the rest of the stuff I'm going to show you.
First thing to do is install Installous so you can get all the free applications you can ever want.Guide here.
Next you want to get Winterboard so you can start getting themes for your device. Guide here.
Now you can add a source to get all of the Cydia store applications for free. Guide Here.
A must have application is iReal SMS 3.0, it lets you reply and send text messages without disturbing what you are doing at the time. You don't need to close your game, Safari, or even unlock your phone. My favorite application. Get IReal SMS 3.0 here now!
