Don’t do it! But nobody listens to that so…
Sit down and work out a prenup that you both agree to. If you can’t sit down and do that with each other then I don’t have to tell you how the rest will work.
Don’t completely pool finances. Have your retirement accounts, working bank account for bills, one for emergencies and one for each of you. In those accounts for each of you agree that a set amount of money goes into them each month and this money can be used for anything you want. This keeps you from having to ask each other permission all the time, lessen money arguments and will help keep your budget on track.
Have separate spaces in your dwelling be it a spare bedroom, mancave in the garage etc where you both can be yourself and enjoy your hobbies without compromise.
It’s not the end of the world if you’re not always having sex or happy with each other all the time.
Plan activities with each other every week. May sound silly at the start of a relationship but as you age together it can be easy to get caught up in careers and your day to day grind. If you are not careful months can go by without really appreciating each other. Contrary to popular belief personality compatibility is more significant than activity compatibility so plan things you both enjoy and be prepared to compromise.
If you can delay marriage live together fo a couple years yes years. Better to know for sure, getting married is easy but getting a divorce is not.
Get to know your inlaws, you’re married to them as well….for better or worse. Don’t ignore this one, I mean it, good inlaws can make a good marriage great but bad ones will utterly destroy it.
Don’t put all your money in the wedding, put it in the honeymoon and your first home together. Some will argue against but if you can do it pick out and purchase/rent your dwelling together instead of moving into one or the others place. This will allow more streamlined compromise. Home is where the heart is so if you’re not home at heart you won’t be in your marriage either.