I grow a lot in a little space. I've currently got a 9x15 foot garden with 12 tomatoes, 10 peppers, 2 zucchini (at least I think it's 2), 3 short rows of beans, and random herbs and such scattered in any open space and pots. Works well for city gardening.
I create a trench system that allows water to be held near plants and moves it around the garden. This is useful in clay soil because otherwise the water just runs off without soaking in.
I use grass clippings as mulch. This is also helpful with keeping my clay soil from getting too dry.
My biggest tip is just try stuff. So far I've not amended my soil much (haven't had time/ money) but my plants do well with fertilizer that is mixed with the water.
