inspect the grout in the typically worst areas, kitchen, laundry, etc. Do a small area or test before the whole floor is spread with cleaner. I like to start with an alkaline, most of the time that is enough. I can't stress how important mechanical agitation is. Running over it with a spinner doesn't always do enough. I like to use a Malish 180 grit brush on a swing machine.
If the alkaline isn't getting it clean enough or doesn't seem right, you can follow up with a quick acid cleaning with phosphoric or something similar.
Let the grout dry to the point it is slightly damp, but not wet. You can color seal over damp grout. Humid is a better term. it doesn't need to be bone dry.
Wipe as you go. The more you have to scrub after you're done, the more chances you have of weakening or damaging the color seal. It dries fast, but takes overnight to really cure and harden. Some brands up to 24-48 hours.