Marriage is a big deal, a HUGE deal, but think about how often people jump into it with someone they barely know. Even marriages between people who do know each other well aren't always successful, because as much as it sucks to hear it, you can't actually control other people. Movies have taught us that true love conquers all, but it doesn't seem to be love that predicts a good marriage so much as communication. Over on Reddit, people shared the things they wish they'd known before getting married, and it's incredibly insightful.
That people often change throughout their lives, but not just because they got married. Many people get married with either the expectation that marriage will change their SO or that the person will stay the same forever. Neither are correct. People will change, but not always in the ways that you expect and you have to be willing to adapt to them.
How they relate to their family and if you can handle it.
If, say, your partner's family is nauseatingly close and loves to spend time together, are you down with that? Is your partner good at setting boundaries?
In-laws can destroy relationships.
Divorces are expensive.
Go to Ikea together. It's like Hunger Games for relationships.
When my grandfather asked my grandmother to marry him her father made them both sit down and write a list of 10 deal breakers. They then had to discuss them all to decide if they could both live with them before he would give his blessing. In over 50 yrs of marriage neither one crossed the deal breaker line and they had a head start on open communication channels from the experience. The other thing they did was to ensure that each of them got at least one hour of me time every day from Monday to Friday (the other would watch the kids and there would be no chores done during that time) and weekends were family time.
Where you're going to spend holidays.
How much time you're going to spend with each family.
Most people don't realize how much stress each other's families bring to the table. Always be a united front.
Pretend you aren't going to have a wedding. Still wanna get married?
Don’t forget to continue going on dates after you’re married
It's probably never going to be 50/50. Somebody is usually going to be carrying more of the load. As long as the burdened partner is not the same one all of the time, you can make it work. Just my opinion.
When you fight, remember that you two are on the same side.
Sometimes it'll feel like it's you versus her... whenever it feels like that, Stop. Back up. Figure out how it's you both versus the world (or you both versus the fear they're feeling, or you both versus the problems you're having or whatever...) and not the two of you against each other.
Hell, try to remember that when you're not fighting too.
If you can't do this... well, I won't say "don't get married"... but do work on this, it's important.