Marriage is a long-term relationship that stands on pillars of honesty. Your spouse should know everything that defines you as a person, whether it is your personality, religion, hobbies or even something as minute as your likes and dislikes. By informing your spouse with this crucial information, you help your spouse develop an understanding of the kind of person you are, which is crucial before you both plan your wedding.
BiWi lists here things every couple must discuss before planning their marriage:

1.    Tell Your Spouse About Your Family Background
Marriage is a long-term bond that is based on mutual acceptance. To become accepted by your partner in a relationship, it is important that you inform your spouse about your family. This includes everything from socioeconomic background of your family to the cast and religion that they belong to. This will also help your future spouse understands dynamics of your family and s/he will find it easier to adjust with them.

2.    Tell Your Spouse About History of Your Relationships
A true relationship stands on honesty and truth. By letting your spouse know all love affairs you had in the past, you will gain your spouse the confidence and trust s/he you deserve in a relationship. No matter how many romantic encounters you had in the past, s/he will respect you for your honesty. Besides, it is better that you let your spouse know everything about your ex-girlfriends before s/he encounters the truth from one of your ex-girlfriends/ boyfriends or husband/wife from your previous wedding which in turn might have serious repercussions on your married life.

3.    Tell Your Spouse About Your Religious Views
Do not shy away from sharing your religious views with your bride and husband-to-be. Your views on religion mean a lot to your spouse and s/he has every right to know your stand on such sensitive topic. Therefore, it is important that you conduct a healthy discussion with your spouse to let your spouse know if you are liberal, moderate or radical in your views about religion.

4.    Tell Your Spouse about Your Encounters With Ailments
If you are diagnosed with an ailment, then it is your moral responsibility to inform your spouse about that. As long as s/he loves you, s/he will not be bothered by gravity of your disease. In fact, s/he will love you for your honesty and stands by you in your fight against the disease.

5.    Tell Your Spouse About Your Bad Habits
We all are born with some bad habits. However, it is your responsibility to inform your spouse about things that might conflict with your spouse’s lifestyle. So, if you have a bad habit of waking up late night or smoking cigarettes, you should tell your spouse categorically about it. S/he will understand it and there are good chances that s/he will help you come out of it.

There are some scenarios where you have no option but to keep something a secret, for example a turbulent past.  There is no point in sharing something from your past with your spouse that has no effect in your relationship today. As long as you love your spouse and you have strength to live with a bitter past, then it is better to not tell those  secrets with your spouse.