Spinach comes in winter and summer varieties and can be sown for a continuous crop of this highly nutritional vegetable where the young leaves can be eaten raw in salads too. 
 
Spinach can be sown directly in the soil in its final growing position with summer harvests being sown in a more sheltered location; maybe amongst taller plants. Winter varieties to be sown in an open and sunny place as it is slower to grow.
 
Dig in plenty of organic compost to the soil bed. Make a drill of approximately an inch deep and sow thinly along it. Later, you can thin out the seedlings. 

At cooler times and locations, you may want to protect the spinach plants in cloches or fleece. 

Spinach can also be sown in containers. 

Both types of spinach like plenty of watering and nitrogen-rich soil. Ensure the soil is always moist. 

Sow at regular intervals for an ongoing harvest; summer varieties can be picked very frequently. Harvest alternate plants to allow space for the remaining plants. 

Sow plenty in April and May and again in August and September for winter crops.  You will pick fewer leaves for the winter varieties. 

Spinach likes the cooler temperatures and will not germinate in hotter summers and plants will go to seed easily. Ideally, spinach likes Spring and Autumn or average summer days. Therefore, protect as required. 

Cooked spinach leaves reduce greatly, therefore pick ample for your needs. Fresh spinach eaten raw is far more nutritious. Spinach leaves do not store very well and so you are better off to pick as you use it.