1.Balance the sweet and sour
Test and adjust the pH of your soil. A $25 pH test kit is a prime investment. If the pH is too low (acid or 'sour' soil) or high (too alkaline or 'sweet'), nutrients can't be released from the soil for use by the plants. Use lime to increase pH, sulphur to reduce it. Getting this right is the first step towards improving soil.
Add dung. Any kind of animal manure is excellent for the soil - fresh or rotted, laid on the surface or dug in. In winter, apply it heavily where needed (you don't need to do this every year) and allow it to rot down and release its goodness into the soil ready for the following spring.
After planting, by all means continue using powerful stuff like fresh chicken manure - but in small amounts, frequently and well mixed into the surface soil. As a general guide, monthly application of a 500 ml container of dry chicken dung per square metre, well spread and mixed in with the surface soil, is about right for vigorously growing vegetables. Brassicas will tolerate more as they are really gross feeders. On mulched ground, lift the mulch, sprinkle the dung under it, then replace.
Water adequately and frequently. Many gardeners just don't use enough water, often enough, and don't spread it widely to develop and maintain shallow feeder root growth. The zone you water should extend well beyond the dripline. Make sure it soaks right in: you may need to push the hose through heavy mulch to ensure the water gets to the actual soil. Penetrating heavy soil with a garden fork will help soakage but don't do this too close to the plants and damage their roots. Even, regular watering is the best way to prevent sudden checks in growth and the infuriating phenomenon of blossom-end rot, which destroys tomatoes and squash just when they're looking good.
Dig in compost or kitchen wastes. There's all that organic material just waiting to become incorporated into your soil. Make a trench along a planting row and progressively fill and cover it. Bones and meat scraps are extra good. Leave this buried treasure in the ground for a month or two before planting on top.
Add gypsum. This is especially useful on clay soils for improving drainage and is also an excellent source of calcium and sulphur that will not affect the soil's pH. Clay soils need heavy applications (follow the instructions on the bag) but on other soils a little goes a long way. The calcium in gypsum is more bio-available so it can fix a deficiency much more quickly than lime will.
6.Dig and turn
Work the soil. In early winter, clear away surface debris and add compost, manure, lime, gypsum, seaweed, etc. Then dig and overturn big clods of earth and leave them. Let the elements to do the work of weathering this until spring, when you can rake it out ready for planting. Hoe your plants (not too closely) to keep up soil aeration, improve water penetration and control weeds.
7.Test the soil
Have a soil test done. Google 'soil testing' to find out the options. Basic but adequate tests cost around $90, an excellent investment if you have a 'difficult' soil or are starting a new garden on land not previously cultivated. Tests may tell you how to correct a deficiency that makes a huge difference to the natural fertility of the soil.
8.Weed out the bullies
Control weeds. Obvious, I know, but they really do snatch the proverbial bread out of the hypothetical mouths of your growing plants. Don't let them bully your green children! Get them when they're small and keep working the soil to discourage them.
9.Mulch, mulch, mulch
Mulch is your best helping hand with weed control and keeping the soil moist. Mulch doesn't just mean plant matter like straw and bark. Stones, tiles, newspapers, cardboard, driftwood and timber are good too. Slugs and snails will shelter under these so turn over occasionally and squash them.
Grow cover crops in winter. Lupins fix nitrogen. Barley draws up nutrients from deep subsoil. Mustard greens repel pests. All these cover crops suppress weeds and keep the soil loose. Dig them into the ground before they flower, or use them in compost.
Mike Bradstock says he seems to have the unhappy knack of continually finding more challenging soils to garden on, and is now applying stupendous amounts of mulch, peat, chicken manure, seaweed, ground-up shell and water to develop a new garden on a sandhill at Raumati South.