If you're going to use your phone make sure you get a flat edge to chock up against the edges of your rims. Make sure you calibrate the software first.
Car also has to be perfectly level. You can do this with vinyl floor tiles, a bucket of water, pvc tubing and a length of wood.
Here's how you do it
When I was in Sydney a mate and I spent the weekend doing the alignments on our cars, following the directions of those videos. My friend had his checked by a tyre shop and we were within 5% of where we wanted to be.