I can't even begin to explain why black and brown dont match. Its the same reason black and dark blue dont match.
Heres a real basic guide to matching, with it, you shant go wrong.
Match the color and material of your belt to that of your shoes. No black belts and brown shoes.
Match your leathers. Like above, but more general.
Match the types of metals that you're wearing. Its either silver or gold, none of that mix and match crap.
Try and stay under 3 colors (Blue jeans and Standard Khakis do not count as colors. Black pants DO count as a color). Four or more colors and you'll look bad.
Be aware of the shades of the colors that you're wearing. Sky blue and navy are both blue, but theyre not the same color. They count as two seperate colors in your wardrobe.
Be aware of your patterns. Checkers and stripes do not go to together. Keep your wardrobe to ONE patterned item. The colors on the pattern do count as colors.
Master the rules, then you may break them. When in doubt, follow them, and nobody shall point at you behind your back.