I love the look of double needle stitching. I just barely bought double needles a few months ago, however. (I may be Princess of Projects, but I'm Queen of Procrastination.) I held off using the needles for a while because I kept forgetting to buy a second spool of thread for my projects.
Until I realized one day I didn't need two spools of thread, I just needed two thread holders. Which leads me to my sewing tip:
When doing double needle stitching, wind a second bobbin to act as the second thread source. So you would have a spool of thread and a bobbin on top of the machine and a second bobbin loaded in the bobbin case. It works great and it saves you having to buy a second spool of bright pink thread for 6 feet of hem work.
(This one was probably obvious to quite a few people, I'll try to make my next tip not quite so easy. )