verbs only
The stress is placed on a syllable as far away from the end of the word as possible. Within reason of course. The Greeks decided that it would not be aesthetic to put the stress on any syllable further than 2 removed from the back, antepenult was fine, anything else was undesirable.
 If at all feasible: antepenult   acute  ἐξλαυνε
 If last syllable is long: penult    acute  ἐξελανει  
 If there are only 2 syllables
     and the last is short:
 acute on 1st (=penult) if short  φρε
 circumflex long drawl on 1st if long   φεγε
So what about καλεῖ , φιλ ? Last syllable is long, acute stress on syllable before, so why circumflex on last? See contractions. καλεῖ is actually καλ ει , last syllable long, acute on penult. Which, if pronounced quickly, turns automatically into καλεῖ . Try saying it yourself and you'll see.