**Edit: there's some invaluable twin needle advice coming through in the comments!**
Remember my metallic Briar I made not so long ago? Well, despite my long-standing flirtation with jersey fabric, that project was the first time I used my twin needle. I was really impressed with the professional finish it produced, so why did it take me so long to have a go? Because trying new things is sometimes scary, especially when you're not sure how involved they might be. Like most things we procrastinate about though, using a twin needle is surprisingly easy, so I figured I'd share some tips to encourage you to give it a go as well.
I use a Brother Innovis 10A - generously gifted to me by Bamber Sewing Machines - which already came with the accessories I needed: twin needle, zigzag foot and extra spool pin. I'm sure these can all be bought separately if necessary though. Different machines may vary regarding some of the steps I'm sharing below, so if in doubt, do have a quick look at your instruction manual.
Step 1: Replace your regular needle with the twin needle - this is exactly the same principle as changing any needle - and attach your zigzag foot.
Step 2: Thread the left needle as you would normally thread any needle, using your regular upper thread.
Step 3: Place your extra spool pin onto the bobbin winder shaft and top with your second spool of thread.
Your machine should now look like this, with the two spools of thread and a twin needle in place.
Step 4: Thread the right needle using your extra spool of thread. Again, thread it in the same way you would a normal needle, but don't pass the thread through the needle bar thread guide this time.
Step 5: Go ahead and start sewing - it's as easy as that! Below I've demonstrated what a zigzag and a straight stitch look like. Pretty neat, no? I used a regular stitch length and tension for this medium weight scrap of jersey, but you may need to experiment with both depending on the thickness and texture of your fabric.
I hope this is helpful to twin needle virgins out there, but if you're a twin needle pro please do chip in with any further advice!