I don't have Di2, but the only general soldering type I usually give is to make sure you're getting the wire hot enough to wick the solder on properly and not end up with a cold solder.

I haven't soldered lately, but I find it extremely calming, like wheel truing or something. The solder wicks on beautifully, everything is nice and clean, it smells wonderful, it's functional. I love it. I always had the prettiest solder jobs in class. Surface mount is a ton of fun too. It looks like it would be hard, but you just put a bunch of solder on, and then wick a bunch back off with a wick, leaving the right amount.

/geek thread