Manure is especially rich in nitrogen and in phosphates as well as other elements. Apply it before growing nitrogen hungry leafy crops like potatoes, cabbage, sprouts, or kale.
YEAR 1: MANURE before potatoes, followed in autumn by: broadbeans, onion sets, or chard.
YEAR 2: then carrots, leeks, lettuce, to go alongside the onions, followed by 'N lifters' to mop-up and dig in.
YEAR 3: Lime if necessary plus garden compost OR; MANURE - followed by brassicas - cabbage, kale, sprouts, etc... and celery, fodder raddish and 'N lifters to mop-up' and dig in
YEAR 4: Comfrey leaves plus garden compost or leaf mold before dwarf beans, runner beans, sweat corn, and 'N fixers' like clover and winter tares to dig in.
Late autumn is the time to apply it to clay soils. These benefit from autumn digging. They are too wet, sticky and heavy to dig by early spring and by late spring it is too late as it should be applied 3 weeks before planting.
Early spring is the best time to dig it into sandy soils as they will loose lots of nutrients during the winter rains of temperate climates. Sandy soils are not as wet or difficult to work in spring.
Some crops prefer it to be applied for a previous crop e.g. carrots, onions, and runner beans. This may be because some crops prefer firm ground not recently dug. Carrots have a reputation for forking if it is applied fresh. I believe this also applies to pelleted chicken manure. Your particular soil type and conditions will effect exactly what you do.
Many crop rotations include composted animal dung once every 3 or 4 years. But your garden can only benefit by applying it more often. My rotation tries to include it twice in 4 years. And now it is so readily available in easy to manage bags I will be applying it around my garden on a regular basis. That includes the flowers, fruit beds and lawns and hedges too.