What is the most important things to have a healthy and strong relationship?

A relationship cannot be kept healthy just by practicing one or two attributes. A healthy and strong relationship needs a lot of attributes that too regularly.

Both the partners cannot afford to be angry at the same time. If your partner is angry, you keep yourself calm. If you're angry, your partner should keep calm. If both get angry at the same time the outcome is always ugly.

Both the partners should be forgiving. Just like when we make mistakes and our family tends to forgive us, the same way we should be forgiving towards our partners for small, unharmful and genuine mistakes.

Patience is one of the most important traits two people need in themselves to be in a strong and healthy relationship. There would come many times where both will feel like they have had enough of drama, but if there isn't abuse or some other major reason, keep patience and wait.

Efforts. It is an easy point to write and tell, but equally hard to practice. Just like you cannot clear all the exams with amazing grades just by studying a few times in a year, the same way your relationship cannot become strong if you put in effort only a few times. There should be consistency in efforts from both sides.

Trust. If you cannot trust your partner and feel the need for constant spying about their life, either you have a set of inner insecurities or your partner is not the right person to be with. Both ways, the relationship isn't going far if there is a lack of mutual trust.

Respect. If you cannot respect the person you're in love with, or if you're not being respected in your relationship, again, this relationship isn't going anywhere.

Space. This is something that needs to be emphasized. Both the partners should give ample time to each other, but also give each other space to grow in their respective lives. Constant communication and excessive closeness, in the long run, will only backfire. Always remember, excess of love and care is also harmful.

Privacy. Keep most of the things that happen between you both private. Don't sing about it in public.

Loyalty. Both the partners can have friends/connections/colleagues from the opposite gender, however, both the partners should maintain dignified boundaries. Cheating has never resulted in happiness in the long run.

Function as a team not as opponents.

Nagging hasn't helped anyone till now.

Never beg.

Advise, don't push.

Communicate, don't blackmail.

Understand, don't harass.

Listen, don't hear.

Love, don't pretend.