mulch is something which covers the ground, with the intent of...
The idea is to fully cover up the earth with a thick layer of organic materials without leaving gaps. By spreading mulches directly on the soil, instead of first converting them to compost, organic materials do double duty - serving as mulch, and as a slow-release of organic fertilizer, soil coniditioner, and worm food.
Always leave a space around the stem of perenials to avoid crown rot fungus. This also applies to trees where a space of at least two feet should be kept. Avoid rich mulch such as strawy manure around young fruit trees, as it creates succulent growth.
Thick mulch over heavy clay on a badly drained soil, may cause acid condition due to lack of air. In winter it also increases the chance of freezing. Maybe add sand.
Alfalfa, one of the best as it is packed with nitrogen.
Oats and hay, have little nitrogen but contain growth hormone.
Weeds contain minerals, make sure they are not too seeded.
Newspaper and cardboard, shredded or layed flat (3-4 layers) and soaked. The ink contains valuable minerals.
Old or scrap carpeting, rug underlay, matting, blankets and quilts. They create perfect habitats for slugs though.
Any agricultural waste.
Coffee grounds from restaurants
Pine needles for plants who like acid conditions, such as blueberries.
Saw dust, but avoid excess quantities as it increases the soil carbon content.
Hair is high in nitrogen and a good insulator for the fibrous surface roots.
Seashells, ground to chips, discourages slugs and snails due to their sharp edges.
Leaves should be shredded, as they readily pack when wet and make leaf mould, which is more valuable tilled in or composted. Leaves have more nutrients, pound for pound, than manure has.
Seaweed is great as it is high in minerals. Use it as it is or washed, and cover it with sawdust or paper
Grass clippings, wooden planks, and anything else that doesn't contain chemicals...