The "Simple" way is to just wire them to your headlight leads in the headlight bucket. This is how most lightbars are connected and saves a lot of time. Some are even wired to the turn signal lights. Big downside: Two more lights put a strain on the 10 amp fuse handling headlight and taillight power. If that fuse blows you lose everything. Headlight, driving lights, instrument lights... Some just put in a bigger fuse but to my mind that isn't a solution, it's a bandaid.
The best way to wire your new lights is to their own circuit. That way if anything goes wrong, like you blow a fuse, you always have some light in front. This only requires a small switch, a 12 volt relay and a bit of wire.
Wire the battery positive (+) to the "30" post of a 12v relay (available at any automotive place) and the other side of the relay (87) to both of your lights. Route the wire right along with the original harness (left side of bike under edge of tank) using zip ties. Suggest 14 or 16 Gauge. Overkill maybe but what the heck. You'll want to put a 10 amp fuse in this line if you are running two 35 watt bulbs. If you ride in the rain a lot you can find waterproof fuse holders at a local boating store.
You still have two other posts on the relay. One (85) goes to ground. If you're putting the relay under your seat just use one of the ground connections available there. from the remaining post (86) run a wire, you can use 20 gauge or maybe smaller for this, right along with your new spotlight wire along the original harness. A fuse in this line is also recommended. The tidy, but not absolutely necessary next routing is through the original equipment tubing, into the headlight bucket and then back to the area of your left hand grip, again through the O.E. tubing (use a piece of wire to fish your electrical wire through). Look carefully and you'll see what I mean. Here (or anyplace you choose) you connect the wire to one side of a small spst switch. Wire from the "other" side of the switch goes back to the headlight bucket where you have several options. My suggestion, connect it to the one wire (blue with yellow strip) that's energized after hitting the "start" button (supplying power to the headlight). This way you have driving lights whether you're on high or low beam. Other options sometimes dictated by state laws are are connections to the high beam or low beam wires. You can check all these with a cheap test light or multimeter.
Result: Turn the new switch on and your new spotlights will come on at the same time as your headlight (after you've hit the starter). You have complete control of when the lights are on or off. As for switch location, there's ample space in the rear portion of the switch box on your left grip for another (two, actually).
Note: This harness can be purchased already assembled at some auto supply outlets and from Amazon. One kit is made by "Pilot" and is part number PL-HARN3 . The kit comes with a lighted switch, relay, and harness with all the connectors you'll need (and then some). Cost is under $25.00 I found one at an Autozone in the aftermarket lighting department.
Above are some common types of relays. For a single set of lights you'll probably used the SPST but look at the others which can provide some lighting options. Note the SPDT can run one accessory when the switch is off (87A) and another (87) when the switch is on. The SPST Dual Make will run two separate accessories (87 & 87B) when you turn on the switch.
Speaking of switches, check out some accessory switch options at Accessory Switch Options.