Always talk to each other about what you want to do in life, your goals, the direction you are moving in, so you can support each other in those endeavors and plan for both individual desires and the needs of the couple as a unit. Talk about these things regularly, at least once a year.
Be responsible with money. Don’t buy anything you can’t afford. Pay off all credit card bills in full every month.
Also, if one of you hates doing something, the other one should do it. Taking out the trash, unloading the dishwasher, don’t fight over these stupid things.
Neither one of you should work more hours than the other, work hours include working at a job and working at home on chores. Split up the chores at home, and reevaluate that split when one of you goes part time or isn’t working, or one of you gets a promotion that requires more time at work.
When you or one of you first gets home after work, spend the first half hour happy to see each other with no demands. Smile, hug and a kiss, small talk.
Know that people usually change a lot during their 20’s, so there might be some growing pains, but I believe almost any couple can make it through if both people have integrity. If you are honest, loving, good people who are committed to the relationship you can be together forever in most cases.
I think the biggest challenge in many relationships is wanting to live in different places, or if inlaws create chaos and the married couple is not a united front. You two are now the core, the couple, your life partner.
Wishing you every happiness! :)