ez man...
I count bars 1 beat 2 beat 3 beat 4 beat = 1 bar 4/4 time... lol
now that the jokes is out of the way...
there are no general rules for this...
In Hip Hop they like 16bar verse 8bar hook/chorus... so that's 8 intro, 16 verse, 8 hook/chorus(which should have been noted in the intro), 16 verse, 8 hook/chorus, 8 out...
That's the simple cut dry...
when you get into other stuff you start noticing pre-chorus, codas, breakdown/bridge blah blah blah...
those can come and go as you need them and develop an ear for noticing that stuff...
a good excercise is to listen to lots of music and notice which parts you are paying the most attention to, and try to note where they are in the song... the pre-chorus is powerful stuff the beatles used it a lot, and some rock songs are starting to incorporate it again, hip hop leans a lot towards the breakdown/bridge where people do there nasty grinding on the floor, or deep hook work.. a lot of room in there to work so... I would say check out a couple tracks you like right down beat for beat where things happen and try to incorprate that format into your work... Don't copy the beat, but the structure...
keep up man.. I hope that helps...
ez,
k