Choose the berry that you want to save the seeds from. Choose your berry seeds from healthy plants with better than average yield. Let the berry become over-ripened until it is squishy.
Place the ripened berry in a kitchen strainer or sieve. Separate the seed from the fruit by gently pushing the ripened fruit down in the sieve with your fingers.
Hold the sieve under the pipe, while running cool water over the berry seeds. Put the seeds on a piece of newspaper or a fine screen. Let them air-dry thoroughly before storage.
Store your berry seeds in a paper envelope. Label and seal the envelope, then place it in a cool, dry area.