How do I collect a soil sample correctly for testing?

You are right, a bad sample gives a useless report, so this matters. Here is the correct method. First, scrape away the surface litter, leaves and stubble from the spot. Then dig a V-shaped pit to about 15 cm (six inches) deep, which is the plough layer, and take a uniform slice of soil from one side of the pit. Do this at 8 to 10 different spots spread across the field in a zig-zag or W pattern, not just from one corner. Avoid odd spots like field bunds, near the well, near manure or fertiliser heaps, near trees, wet patches and old paths, because these give wrong readings. Put all the small samples together in a clean bucket, break the lumps, mix thoroughly, and remove stones, roots and trash. Spread it out and use the quartering method, divide into four, keep two opposite quarters, mix again, and repeat until you are left with about half a kilo of soil. Let it dry in shade, never in the sun or over fire. Put it in a clean cloth bag with a label inside and outside showing your name, village, survey or khasra number, date and the crop you plan to grow. Keep separate samples for fields that look different or grow different crops. If you are unsure, ask your KVK to show you once, then it is easy every time.