You want zero ammonia and zero nitrite (that means the tank is "cycled" - check out my article in my sig if you're not sure about that).
Nitrate should be <25 ppm. If its at zero, something's wrong (like your tank isn't cycled or your test kit's naff).
For a general community tank, if you're getting fish locally whatever pH you have should be fine as long is it's pH 6 - pH 7.5. But I've got one tank of tetras and a betta at pH 8.5 and they're fine (the tetras are black neons which are pretty tough and they've been at that pH forever). The main thing with pH is that its stable - don't be tempted to mess around with it, particularly if you've got hard water.
KH and GH should be as they come out of the tap - unless you have discus or Malawi cichlids (soft water and hard water respectively), don't worry about it. Just be aware that a high KH means the pH is more stable (which is a good thing normally but a bad thing if you're trying to change the pH). A high GH is annoying because it chalks up everything.
