Short answer - eat some food, drink some water, do a little bit of walking.
I did a 10 mile race yesterday, so this is what I did after finishing:
Had the Snickers bar and orange juice they gave me. Walked back to the car, had a banana and some water. Walked around slowly and took some photos for about 20 minutes. Drove home, drank some more water on the way.
Got home. Had a mug of hot chocolate and a handful of Pringles. Had a bath. Had my normal lunch (beans with random bits of meat in it and bread), drank more water.
Spent most of the rest of the day playing video games and watching TV. Iced my knee 'cos it felt a bit sore, found a small blister so I put a plaster on it. Had dinner, more water and another hot chocolate.
Today, went to work. Went for a walk at lunch time (about 20 minutes), ate and drank as normal. I may go to the pub this evening. Might ice my knee again, although it seemed OK this morning so I probably won't bother.
Usually I run Tuesdays, Thursdays and Saturdays. I'm going to skip the Tuesday run, and probably do the Thursday one. Will parkrun on Saturday but expect I'll take it fairly easy. I wait until everything stops aching before I run again, which the first time I did a HM was about a week, but 2 or 3 days is usually enough these days.