Here are the generalizations (but don't hold true for every post rock band):
1. Songs are very long and you will be totally drawn in (though for starters I would recommend EITS first to get the taste)
2. Mostly instrumentals (by that use of many instruments gradually and possibly eargasmic crescendos).
3. Multiple eargasms due to varied set of emotions expressed in the song.
4. If there are vocals then they will flow with the music. Hear to Untitled 5 by Sigur Ros.
5. Best way to think about anything while listening the post rock.
6. A complete album is like a journey and songs are seamlessly related in sequence or atleast appear to. You start imagining your own wordings and story to the music and that makes it a personalized experience.
Start with
Explosions In the Sky's album named
The Earth is Not A Cold Dead Place. If you like then i'll pour some more.
PS: Today is my lucky day. More on it late in a thread