You need to rotate most things around to reduce the risk of plant and soil diseases. Have a search for vegetable crop rotations to get some ideas. Plants like broad beans and other legumes are fantastic plants for putting nitrogen back into the soil - on their roots they develop nodules which look like little lumps along all the roots and if you can get this to happen, then you're doing it right and they will put essential nitrogen back into the ground without you having to add it yourself artificially.

Most of all you really need to have a think about what types of vegies your family eats - not much point in growing something that you wont eat. Plus you may get a bumper crop of something (Like we did with our broad beans and peas this year - I didn't buy peas for nearly 2 months and I still have several kilo's of broad beans) and you may need to look into preserving it so 1 it doesn't get wasted and 2 so you can eat it out of season. Some of those things are really hard to grow well - like carrots and garlic. Garlic takes a long time to mature so it's not something you're going to get a reward off straight away. And carrots are just soooo hard. We try them every year and we have problems with them every time, from either being eaten by bugs or them just not growing big enough etc. We only have a small vege patch set up atm, it's probably only 6-8mts sq, but it's more of a hobby for DS than anything else. But we have plans to set up a much larger one when we have the funds to extend the watering system