Grietjekarwietje: Het netjes afwerken van je haakwerk - This is a cool way to do an invisible join. The page is in Dutch, but can be translated by clicking an icon to the right. There are also photos which clearly show the technique.
Demystifying Double Crochet for Beginners - this tutorial shows you exactly what to do when you come to the end of a dc row so you don't miss a stitch. Many beginners forget to stitch in the turning chain.