Express your feelings in an honest way. If you're concerned that your partner doesn't get along with your relatives and both of you are planning to marry soon, sit with her and discuss these issues. Mention that you don't understand the reasons for the tension and ask her why she doesn't like your family. Maybe your relatives have already prejudged her without really getting to know her and she's hurt by this.
Prove that you can be trusted. If your partner feels strongly about loyalty in a relationship and he told you some painful secrets about his abusive childhood and struggles with drug addiction over the years, don't tell your friends because this will make him think you don't care about his feelings. Or if your partner has been feeling like a failure and depressed because of a big mistake she made at work that caused her to lose her job, keep the details of this incident to yourself and cheer her up.
Show generosity and gratitude. If you know your partner has been wanting to attend an upcoming local chocolate tasting but can't afford it because of tight finances, give him tickets as a gift and go with him to the event. Or if your partner has been generous by letting you use her car to get to and from work, express your gratitude by planning an evening out at her favorite restaurant.
Apologize and forgive when necessary. If you offended your partner by saying hurtful things about his physical appearance out of spite, apologize and resolve to handle your disagreements in a more respectful way. Or if your partner apologized to you for not paying her half of the rent, forgive her and work out a reasonable agreement that will allow both of you to equally contribute to the household.