Alot of ways to do it and steps to take---but the steps are quite simple, in and of themselves:
1.) as you suggested, wash them with soap and water----to start
2.) trim/clip your toenails, so there is about 0.1 mm of "the white part of the nail" left over; trimming too close to the skin can actually cause ingrown toenails (which is a whole other problem in itself)
3.) pay attention to early warning signs of foot fungus and/or toe fungus (Lamisil or Lotrimin usually solves it)
4.) watch where you step, especially in public places like pools, showers, gyms, etc
5.) scrape your heels, the side of your big toe, and each of the 5 "pads" on the bottom of your feet (ever heard of Ped-Egg? It really works and it's less than $10 at Wal-Mart)
6.) moisturize your feet/heels at night with Vaseline (or some other foot ointment or moisturizer) and sleep with socks overnight [the socks act like a "greenhouse" and keep the moisture in your skin, doing this repeatedly for about a month or two will eventually give your feet their own balance of moisture---in which then you can cease applying moisturizer]
7.) try to get a pedicure once or twice a year, or at the very least every 18 months
8.) let your feet air out, and don't be afraid to remove the dead skin with rubbing alcohol (also good for circulation in the foot)
9.) by all means, wash off the black (or other color) ink off your feet that accumulated from your sweaty feet & socks you wore the day before or last week [if your feet are still colored from ink from last week's socks, that's just trifling---but some of you know who you are]
10.) last but not least, wear slippers or sandals around the house and don't walk outside barefeet [some of you know who you are]...it's already bad enough you don't clean/care for your feet, but the added dirt from the floor/ground is not gonna help any
As you can see, these are very simple steps to take, doesn't require lotsa money or medicine/doctors, and most of them you can do while you are in the shower or sitting around watching tv, etc