Saving your own seeds, is only recommended for unusual or rare open pollinated varieties. A surprisingly large number of older varieties of vegetables are becoming difficult to source, as it costs the Seed Companies large sums to keep them registered with the EU. Generally, if you shop around, you can buy the common varieties of seeds, quite cheaply.
Never save seeds from F1 varieties, as the seeds will never come true to the parent plants.
Separation distance of your parent plants from other varieties. You need to make sure that your parent plants, that you are gathering the seed from, are a good distance from similar plants on your ground or your neighbours’ ground. This is because they will be open pollinated by the busy little bees, and you do not want the pollen being transferred from these different varieties to the variety that you are growing for seed. You can sometimes spot this problem if you see the flowers, or the seed pods are not of the correct type or colour for the variety that you are collecting.
It is difficult to quote a separation distance, but I would start with about 20 m, but more would be better.
If saving seed from peas and broad beans, do not leave the pods on the plants for too long or the mice and squirrels will eat the lot. Harvest the pods and let the pods dry naturally in a safe place. Once the pods are fully dry, you can then shell the pods and save the peas or beans.