Top tip. When attempting to sew a cushion cover, if you have just put in a zip down one side and are feeling quite pleased with yourself. Before putting right sides together and sewing round the other three edges, it might be an idea to open said zip. Otherwise, as any numpty can plainly see, you are going to have extreme difficulty turning the thing inside out. Leaving you with something that is neither decorative nor useful. *Reaches sheepishly for seam ripper*.
I had hoped I could accomplish a simple cushion cover without recourse to an internet tutorial, but clearly I still need google to hold my hand through this area of textile adventuring.
Maybe I should change my name by deed poll to once-rubbish-now-probably-fairly-average-knitter-but-still-mindbogglingly-thick-at-sewing. Catchy! I bet that userid is still available on ravelry too.