I stuck all my wiring at the back of the headlamp beside the battery, it makes it easy to get the live and earth, stuck the relay there with fuses both in the live feed from the battery and the live from the main beam headlamps just in case. Use the proper graded cable for the spots, not poofy stuff that will melt and see if you can get some heat shrink for the conections to keep the water out. Aldi's were doing a box of them.
I just stuck the fuses into spades but it's best to invest in a small fuse box from an assessory shop, or a couple of water proof tube type. Remember to stick in a heavy duty relay. On the relay side fit a smaller fuse from the headlamp feed, "the one that energises the relay" that way if the spots go bottoms up only they blow and not all your headlamps as well.
The spots come with fitting instructions and if you fit them as to come on with headlamps then they should be fitted as per the instructions, i.e the required distance from the outer edge of the vehicle and height from ground. If you don't care then just bang them on any place, I see many like this.
Best to pull the fuse out during M.O.T it saves ****ing about with alignment, therefore they are not tested. I set mine to light up the world, and they are never going to pass the test so I pull the fuse out.