My steel (Reynolds 631) Bob Jackson that I built up myself I treated internally with Framesaver, the outside gets a coat of wax periodically, I keep the seatpost well greased and fill the groove at the back of the seat tube/clamp area with grease to help stop water getting in there.
The bottom bracket is a Cinelli spoiler so has cut-outs that allow water to drain that way.
The bike is stored in the house and I leather it off if I come back from a ride wet. It also has guards fitted of course, as much to keep the bike clean as to keep me clean.

Having said all that I don't know of anyone who has had a reasonably well cared for steel frame fail due to rust. It helps to cover any paint chips with something like clear nail polish. I love good carbon and alu frames but I would expect to get through several of either in the lifetime of the steel frame.