I guess LB that you do it the old fashioned way- by speaking to friends, family, their friends, etc. who are in shidduchim or recently married and get recommendations from them.
As far as Rabbis/posek, again, word of mouth goes a long way. For example, maybe there is a family that you feel close to that you admire the way they live, and you can ask them who their Rav is, and see if that is someone you can relate to. Also, you can ask your teachers for a recommendation, or chose one of your teachers who you admire and already know- for many BTs, this is probably the most practical way to find a Rav. Aseh licha Rav is not easy, which is why I think there are a lot of people out there who do not have a rav, but would like one.