These are always hard to answer because we've no idea how much or little you already know.
At a minimum download the assistants and make sure you've the latest firmware in the Vision and the controller.
Read the manuals (available on line).
View the DJI (Colin Guinn) YouTube tutorials if you can find them.
Spend as much time as you can looking through the forum's topics that seem related to flying.
If you're a total novice, perhaps read this overview -
http://www.lsvl.info/Phantom2Vision.htm .
Make your first flights in the biggest space you can find.
Before starting the motors, give it plenty of time to do its pre-flight checks and get GPS and home lock (learn the light pattern to look for - depends on the mode you're in, Vision 2 vs. NAZA).
As soon as you lift off, stop at about 6 or 8 feet, and just let the Phantom sit there for a minute or so until you're convinced it's got its act together. Get a feel for how well it holds position (depends on wind, number of GPS satellites it "sees"). If it doesn't stay within about 6 feet of where you "parked" it (no control inputs), land it and redo the pre-flight (either something didn't complete or it's just too windy).
Make your control inputs slow and small at first so you see what a given input results in. The exception is at take off ... don't try to "ease it off the ground" as you may tip it and damage the rotors. You can pretty safely give it almost full power until it actually lifts off then immediately cut back.
Don't go zooming far or high until you feel comfortable with it. Remember that the farther away it is, the harder it will be to see what its doing.
If you're up fairly high, don't attempt to descend vertically very quickly. The Vision (like any 'copter) can get caught in its own prop wash and bad things will happen. If you must descend very quickly, add some lateral movement so it stays in fresh air.