In your opinion, what elements can lead to a successful marriage? present at least two paragraphs.

Communication is a very big element, no matter how small. If an argument arises-try to use prior knowledge of your lover`s mood and ideals to calm the situation down, tell them what they want to hear even if it means a loss for you.
If you have kids, be sure to do your best in being in their life and helping your Other care for them adequately. Support is also a big element especially if your Other is going though something or trying to pursue something. Do the best you can to be there for them.
Keep weigh of your Others emotions-know the signs of depression(social Isolation, lack of motivation, substance abuse, etc.) and confront them gently about whatever may be wrong. 

It hurts for them at first then they get used to it