Consider what it means to have a better relationship? In my opinion, it’s simply having a happier and enjoyable life. To do so you must improve your life in two aspects: 1) as friends and partners who spend a lot of together, make each other's life happier. 2) As a couple who have specific and exclusive roles toward one another, make life more enjoyable.
For #1, I could say that you should find activities that you both enjoy. Communicate honestly and openly with one another. Be playful and carefree in everyday life. Have shared interests and hobbies.
For #2, talk about how you feel. Have common goals and become each other's allies. Remove negative habits and work to improve yourself and each other. Be caring and supportive. Show that you appreciate each other. Show intimacy and affection.