There's a power block on the left-hand side of the battery, under a plastic cover - it's got two big bolts. Run some decent gauge wire from that (gives you both + and - ), and use a fuse in your wiring (5A, 10A - whatever is appropriate for the gauge wire you use). You can get a blade fuse receptacle at most auto parts or hardware stores, that way you don't have to stock multiple different kinds of fuses.
If you want switched power, you can find a supply to the fuse block. The block can pull free from its mounting, and you can access the underside. Pick a supply wire to something switched other than the low-beam fuse (that switches off when hi-beams are on). You can determine which side is the supply to the fuse with the wiring diagram, or perhaps more easily by using a voltmeter, pulling the fuse, and seeing which side of the fuse receptacle reads 12V when the ignition is on.
Once you've found the hot supply wire, tap into it with one of the 3M wire taps (or similar). Again, make sure to fuse that line.
Apparently there's also a power connector for the OEM heated grips hidden somewhere in the cowling - already switched and fused. Search the site or the web to get details on that (I found out about it after I'd already done all my forward wiring - go figure).
'07 DL650 ABS
'04 Yamaha V-Star 650 Classic Silverado (gone)
'04 Yamaha TTR225
'03 BMW F650GS (wife's)
'92 Honda XR250L
'86 Honda VT500c (gone)