One a week on saturday or sunday would be good enough. Use a
normal rag and a shammy cloth for light scrubbing. Old used
toothbrushes are good for scrubbing the rims. Get those car washing
detergents like selleys at NTUC will do.
Wet the car, go on with soaping and rinse thoroughly with water
about twice and dry it thoroughly with a seperate rag as the
minerals in tap water will leave a faint residue with marks.
Polishing need not be frequent, say once a month, once again, a dry
clean rag would do nicely.
Remember to use a moist rag to wipe the car interiors as well. Keep
it dust free. Same goes for the floormats, dun be lazy, take it out
and give it a washing down and let dry or a vacuum. 
