Does this mean I am using the wrong size hook? I am using double knit yarn, and a 5mm hook, because that looks like the right size of actual hook to grab the yarn, if you see what I mean (I don't actually know which hook sizes to use for which yarns).
I have managed to follow the patterns in my crochet books, and learn some new things, but it doesn't look that good, because it is all loose and baggy.