Vegetables are divided into three groups - Roots, Brassicas and Others.
Usually manure is applied in Autumn but life sometimes gets in the way. Not all crops need manure, infact it badly affects the performance of some. Carrots for example don't like too much fertility, manure makes them fork and gives you multi legged vegetables that are impossible to peel. The best thing for carrots is a mix of sand and compost. I didn't have time to fill up the whole bed with sand and compost mix so I cheated last year and when it can to sowing time used a big dibber and made a hole the size my ideal carrot would be, filled it with compost/sand then sowed couple of seeds in each hole at recommended depth. It worked brilliantly - had decent sized carrots for once. The other way you can do it is to make a trench and fill it with compost sand mix then sow as recommended on packet. The other plants that don't need manure are beetroot, chicory, jerusalem artichoke, parsnip, salsify, scorzonera, marrow, peppers, tomato, cucumber, onion. These are all root vegetables or are grown with root vegetables.
For brassicas dig in well rotted compost or manure preferably in Autumn but if not early spring. By manure I mean well-rotted stable manure - to put it bluntly it nolonger looks like poo but is crumbly and doesn't stink. Brassicas include cabbages, brussel sprouts, cauliflower and kale. Lime before planting as helps prevent clubroot. They like firm soil so push the ground in firmly with the heel of your foot around seedlings when you plant them.
Others includes beans, peas , sweetcorn, celery, , lettuce, swiss chard, okra, spinach, globe artichokes.
For potatoes I just add the manure when I am planting them. not sure if that's what you are emant to do but works for me.
So plan what you are putting where and then make sure you have manured the bit for the brassicas and others.
I will endeavour to explain crop rotation tomorrow if I haven't put you off. I want to get a hacksaw to my plastercast but will not.