Right guitar positioning is the one that feels natural and comfortable to you, your muscles are relaxed and there's no unnecessary tension. Often, beginner guitar players lift their shoulders in a strain while not being aware of it.
The best way to learn to hold a guitar is to watch yourself in the mirror and work out getting away from all the tensions. It's also worth to do when you'll begin playing, for some time in order to gain good habits.
I recommend to learn playing in both a sitting and a standing position.
When sitting, I used to put the guitar on my left leg as in classical guitar positioning, because I first started to play a classical guitar. But many folks find it more comfortable to put an electric guitar on the right leg like in the picture below.
If you choose to play in the classical position, put some hard stuff beneath the left foot (or right one if you're holding a left-handed instrument), it can be a footstool, a piece of wood, or a couple of thick books. This will make playing much more comfortable.
Whenever you play, your hands must not help to hold the guitar, they should be free to play.
When you stand, use the guitar strap to hold the instrument. The strap goes from the top strap peg, via your left shoulder, diagonally across your back and returns to the second peg on the guitar.
Don't put the strap over the head like a neck chain, it's uncomfortable as heck and looks stupid too :)))
Now when you've got acquainted with the guitar positioning let's put the hands on the guitar. The left hand is the fretting hand and the right hand is the picking hand.