My Green Thumb Is Brown Much Like The Flowers I Tried To Plant- HELP!

I have a great backyard that I would love to be covered in flowers and other pretty green things. However, in reality its more like a sad little flower graveyard. I just don't get it... I plant them, water them, LOVE them even and nothing. So, what am I doing wrong? Do you have a great tip you could share with me? At least do it for the flowers, the poor innocent flowers that I will keep buying and unintentionally killing. Is there a potting soil you recommend or a certain type of flower that might make it around my house? I'd love to know what you think ! In the mean time here's some great places to check out here in Amarillo for all your gardening needs. Mine have just consisted of trash bags and a feeling of failure lol.

http://www.petesgreenhouse.com/

http://www.coultergardenamarillo.com/index.htm