My opinion about this has changed greatly in the last two decades, but if I were giving this advice to my very own daughters I would tell them this:
1. find someone who is intellectually equal to you (or very close)
2. find someone who unconditionally adores you
I believe very strongly that love is more of a choice than a feeling. Both of the above have managed to be the two things I consistently fall back on and realize are the reasons my husband and I have maintained such a dynamic but ever deepening love relationship.