If you accept that there's two of you in the relationship, and that you both have to make an effort consistently, then most of your relationship should be mainly smooth sailing.

In my opinion a lot of people fall into the habit of allowing things to get stale by not making a effort anymore, they become too comfortable and they get lazy. Example of this are things like letting yourself go, and when you stop actively wooing your partner. Yes it takes wirk and effort, but if they effort was worth it to land Him/Her in the first place, why do you stop making that same effort?

Another thing most people misunderstand is what a compromise actually involves. A true compromise means neither of you get exactly what you want but instead you both get some of what you want. The mistake too many people make here is agreeing to a "compromise" that they don't see as being fair, and they agree just for the sake of peace.

I'm married 20 years and like most couples my wife have had our ups and downs. When we look back on where we had the downs, we both agree it's nearly always related to a lack of effort by one or both of us, and anytime we both start making a consistent effort things massively improve.