You want a spot that receives as much sun as possible. The closer to you front or back door (zone one) the better, that way you will always see it and by default you will know when to harvest, if the mulch needs topping up, if it need more water, when to replant, as well as other interesting observations.
When you have decided where you will grow the next thing you need to do is, to aerate the soil by double digging, using a broad fork or by using a small rotavator. Having clearly defined permanent paths is important, as it's best to not walk on your veggie beds and avoid compaction. I always add aged manure when de-compacting the soil on beds like these, cow manure is best.
I also add two additives; rock dust and sea-weed powder. These are inexpensive and can easily be brought on-line in 4 or 5 KG bags. You could also add blood and bone powder. These are sprinkled on the beds.