I’ve met a lot of people that looked like good matches that weren’t. Some things on which you’d better agree upon up front that I’ve noticed have been big problems for some:
(1) Children: How many and what kind of schooling. If you want a daughter to be able to learn all the halachic sources but your prospective partner thinks that is a waste of time, that is a problem. Similarly, of you think a son should only learn Torah but your spouse wants him to have a choice of careers that is a problem.
(2) Where to live: Some people just won’t consider leaving the NY metro area. Other people are called to make aliyah. This can be a deal-breaker.
(3) Career plans: If you want to learn full time and she doesn’t want to work outside the home, you’d better have an independent source of income. In general, lifestyle must fit income and both of you must realize that. Most (not all) careers that generate good income require advanced secular education; my wife and I both have earned doctorates.
(4) Chumrot: If either of you will give up your favorite chumrot in the interest of shalom bayit, you have a problem.
(5) Willingness to go with the flow: HaShem sometimes gives us things we did not expect. We must be willing to take whatever comes, and be flexible. You and your partner should realize that the plans are made by HaShem, and not by us — and be willing to react accordingly.
Then there are things that really don’t matter: What kind of kipah you wear, whether you wear a wig or a headscarf, and other surface things. It is the insides that matter.
I was blessed to find a tzniut woman with good midot who shared my values; I asked her to marry me on the second date. We had met through frumster.com. Baruch HaShem we are still married 5 1/2 years later.