ph - you need to do the high range, if your reading is on the top of the low range test. pH doesn't need to be perfect necessarily. Somewhere between 6-8 is probably fine, so long as you keep it constant. Do not use pH modifying chemicals.
Ammonia - ideally 0 ppm
. If your tank is cycled it will be 0 or near 0 all the time
nitrite - ideally 0 ppm
. If your tank is cycled it it will be 0 or near 0 all the time
nitrate - 0-40 ppm
is safe. If you grow live plants, you want somewhere between 10-20ppm. Up to 40 is safe, but if it gets the high, a water change or 2 will bring it back down to a normal level.