watering stuff

this is probably a really stupid question, but how often should i be watering stuff. i'm very new to all this and i'm not really sure what to be up to. i've got peas that are growing, and seem to be doing quite well, onions that seem be thriving, and purple brocolli that seems to be sprouting everywhere. these are all outside, along with Carrots and Parsnips that are seem to be sprouting in an old bookshelf that i turned on its side to beet Carrot Fly.

 in my little plastic greehouse i have runner beens that are shooting up quickly, Corgettes that are getting really big and flowery, as well as turnips, Cauli's, chilli, strawberrys and tomatoes, all of which seem to be doing ok, although as this is my first attempt, i have no previous form to compare any of them with. i have also recently put some squash seeds in, and have sweetcorn and leeks growing away on the windowsills in the kitchen

but since i have started this, there has been precious little rain, i'm giving them all a sprinke with teh watering can in the evenings, but should i water some more than others, can i water some too much or not enough??

cheers