hmm, to a nt, this suggestion might be overkill, but then, you arent a nt: you could try searching the web for color theory basics. mainly things like complementary contrasts, split contrasts, etcetera...
a few base rules (as bruce lee said: follow the rules without being bound by them):
-every color matches black (read: black trousers are a good investment because all kinds of shirts go well with it)
-same goes for white
-avoid colors that are too close to each other (for example, several slightly different shades of red, each with a different texture like matte, glossy and velvet - extremely important when choosing an outfit in one color)
-as soon as colors are apart far enough to be identified as two different colors (denim blue and greenish blue for example), neighbouring colors make a harmony.
-complementary contrasts are tricky to pull off (green-red, blue-orange, etcetera), but not impossible. keeping one color more subdued than the other makes it easier. two intense complementary colors (candy pink plus neon green) are bound to look eighties - in a bad way.
-different patterns should not be combined: dont mix polka dots with stripes
-a solid color plus one patterned item always works (keeping its colors in mind, of course): solid shirt with striped or dotted tie OR patterned shirt with solid tie. mixing patterns is trickier.