It need not be fancy or store bought. A plain loose-leaf notebook will do. But, whatever you do, keep a gardening journal.
Cut out garden layouts and pictures you like from your magazines and paste or tape them in your journal. Note the names of plants that you may want to try out.
If you’re computer savvy, you may want to keep your journal online.
Date each entry. During gardening season, note what you planted where; including the dates when plants come into bloom.
An actual journal is best for taping down empty seed packets and plant identification tags.
Note when you plant new purchases. Make simple diagrams of your garden. Take photographs and scan or paste them in. Come next year (or next planting season), you’ll be glad you did.