I usually calculate my mash temperature (using Brewzor on my phone) and then heat the strike water about 5 degrees warmer. I dump the water in, stir it, and I am always pretty close to what my strike water is supposed to be. Once it gets down to that temperature, I add my grain and mash as usual.
IMO, its easier to take heat away than add heat, so I prefer to have my strike water a couple degrees hot.