Being an old married fart, generally once a day although like most old married farts it depends a great deal as to what's going on. Some days I'm just far too busy to take the time to take care of business as it were.
Generally I use some sort of visual aid so I look up pics on Facebook or elsewhere, and fap away. Sometimes I'm in a seated position, or sometimes prone in my bed. Depends on opportunity and mood mainly. I don't really use a single technique (overhand or underhand) although sometimes I'll use a sock or a washcloth. Since I do the laundry in the house I don't feel guilty about such things. Too much information?