Personalizing the cover of the journal can be easily done with stickers, collage, or paint. We prefer to plaster the cover with stickers that we get from various places. Someone once remarked that the journals are like the old steamer trunks with their labels of the places they've been.
And so, the cover of the journal can become an extension of the journal and the journal keeper by containing evidence of places, personality, and interests. So think about how the cover of your journal reflects the person you are.