mixing hardstyle means you've got to know the records. Well.. if you want to mix properly right and like it's supposed to be mixed.
Mostly it's mixed on the first beat out of 4.
Producers often keep this in mind while producing the records. (especially saifam productions (for the technoboy sets :P)
Hardstyle is all about building tracks and sets to a climax.
I think it's best when djs skip the first part of a record. It's not appreciated to hear a 6/7 minute song. Make sure you only play like 4/5 minutes of it.