Storing seed is easy. Here are a few tips:
- Save seed only from the best, healthiest plants
- Save only the best, healthiest seeds
- To minimise the risk of cross pollination, take seeds from plants in the middle of your patch rather than on the edge.
- Leave the fruit on the plant to fully ripen before taking the seed.

There are lots of good books on saving seeds. My favourite is Back Garden Seedsaving by Sue Stickland.