You could google pillowcase dress for a tutorial. It is a pretty simple dress with very forgiving shape and technique. There are hundreds on the web.

Otherwise, prudent baby is a good place to go as Tanstar mentioned.

ETA: Prudent Baby actually have a pillowcase dress - super easy.
After a quick look through some of my bookmarks I found "Make it and Love it - Paperbag skirt" and "Sew Mama Sew - yoga skirt tutorial" both really easy sewing.