Be nice and polite to each other and don't use harsh words. Be supportive in all ways (as long as it’s rational). When talking about something that displeases you, try to mention it in an objective manner. Once in a while go out and have fun together! Challenge each other by sharing exciting goals and dreams and working towards them together.
Most aspects of marriage are somewhat tactical and methodical, in terms of communication and conflict resolution and so on. But I guess what sweetens the relationship is the act of love and affection that is shared between the couple, a sort of bond that is special and unique. It's the kiss that a couple shares before they go off to work, as well as physical intimacy. Without these, the marriage can be somewhat dull.
The best way to sweeten your relationship is to renew the connection between you. Start by honoring each other with deep respect and special attention. Little gestures like a flower for her and delicious supper for him cooked with love, can rekindle the love between you. On this level sweetening the relatioship equals a deep connection between spouses.
A little bit of time and attention can help any couple sweeten their marriage. Most marriages are burdened by a mountain of tiny conflicts that can build up over time. The salve that heals those wounds comes from a strong emotional bond between a couple. You can improve that bond and sweeten your relationship by attending to the romantic needs of your relationship and maintaining a friendship with your spouse. Consider having a regular date night or going away for a weekend retreat at the beach or in the mountains. Do fun things together. Laugh and enjoy each other’s company.