Green thumb? Not so much....

I took my $50 gift card to Home Depot and bought plants. I plan on buying a home next year and it's time for me to learn how to take care of various vegetation so that my yard won't look pitiful. So far I am failing miserably. My first victim was a ground cover plant that looks completely fried. The care instructions say "full sun" but now I'm not so sure. I have repotted it and we'll see if it comes back. Next is an African Violet I brought to work. Ok, these are supposed to be impossible to kill! But I think I overwatered it. The leaves still look good....but the flowers are completely gone. Hopefully I have not sent it to it's maker. The third and final victim (so far) is a yellow mum. Again, the instructions say "full sun" but the flowers are almost all dried up. I can't figure out what I'm doing wrong! As an environmentalist, it is quite disconcerting that I can't get my little green friends to stay alive for me. I feel like Charlie Brown and his Christmas tree....."I've killed it! Everything I touch gets ruined!"