Depends on what kind of cycling you do, but I usually just use a piece of micro fiber and wipe down the dirt and smudges off the down tube/seat tube/chain stay(riding in dry weather).
Every 2 weeks or so I would clean my chain and lube it up.
Every 3 months or so I would do an overhaul(I'm a lazy person).
Back when I used to ride in all weather I bought one of those Simple Green bike cleaners, they worked well.
Soap and water will work just as good if you don't led the dirt and grime sit for a long time.