The best way to do it is coat the pan in a skim coat of lard, and bake in the oven, at 350 degrees for a while. This will "seal the pores" and prevent rust and "stickage".
I don't know how others feel, but I never use soap to wash my cast irons, just some hot water and a sponge/towel, and wipe it out well...
Solid shortening works really well. If you have rust use steel wool to get it out first. Then put the shortening on the iron piece and put it in the oven at 375 for 45 minutes, then wipe it out and do it again.