While a lot of pop, modern astrology explains compatibility based on the Sun sign, that is only one piece of a larger relationship puzzle. Though to me, looking only at the Sun (or Moon), leaves a lot to be desired in my book of love. The Sun in our natal charts represents our outward personality, identity, and how we want to be seen in the world. While the way we present ourselves and how we want to be seen is a part of it, there are many other facets to pay attention to when it comes to relating and compatibility.
What is compatibility between two people? That is the ultimate question. Of course there are many theories, here are a few of my favorites:
Though for me, many of these patterns of compatibility reveal themselves in certain archetypal patterns in the natal charts or synastry between two people or composite charts. These patterns, or in this case planets, give us a better understanding of the lessons or healing between two people whether that be romantic partnerships, business partners, or even family members. I also believe there are "types of soulmates" that reveal patterns of these relating. (More on that here.)
LEARN MORE ABOUT COUPLES CONSULTATIONS HERE.
I pay the most attention to personal planets or asteroids because they are closest to us in the solar system and also move the fastest, as well as how the social planets (Jupiter and Saturn) relate to them. There are also several "sex" or erotic asteroids I utilize in chart comparisons, but I don't go into that here.
Here are the main things I look at between two charts (synastry) and in the composite (a combined chart of two people):
Moon :: unconsciousness needs, attachment style, home life important to know when living with someone, internal rhythms and sense of self
Sun :: outward personality and identity, how you want to be seen in the world, do your identities match or is there a clash of ego?
Mercury :: communication style, intellectual stimulation, can you hear each other and communicate easily
Venus :: love language, love style (see above), feelings of compatibility
Mars :: conflict style, turn on, or how you move in the world
Juno :: what motivates you to be in partnership, what is non-negotiable
Descendant :: type of relationship/container (read more here)
I'm not going to tell you all my secrets about what I look for within these...for that it makes sense to schedule a Couples Consultation.;)