More on pronouncing Greek words:
"There are different systems in use for deciding which syllable of a word is to be stressed. It is best simply to take care to pronounce each syllable clearly (particularly to be careful to distinguish the long and short vowels), and then let stress take care of itself" (J.W. Wenham, Elements of NT Greek, p. 23).
Donald Mastronarde gives the following examples of accentuation in Attic Greek:
ἀγαθός- "Short U[ltima] accented with acute, in isolation (no mora) follows the contonation on U[ltima]."
A "mora" is the so-called standard "length of a short vowel" such as A, E, I, O, U and final AI and OI in most cases (p. 17-18).
ψυχή-"Long U accented with acute, in isolation (no mora follows the contonation on U)" (Mastronarde, p. 18).
For what it is worth, I was taught that pronouncing accents is not an exact science. We are so far removed from Koine or Attic Greek that there is no way to be sure just how the syllables were stressed (pace Caragounis). Like Wenham, I'm inclined to say that one should place stress on Greek syllables, as best he or she can. Nevertheless, I must say that it is somewhat fun to read Greek poetry metrically.
In my Greek poetry undergrad class, we used to scan meter and that really helped us to stress syllables precisely, but it was difficult to me. The exercises we did were akin to breaking down English words like to-day or diff-i-cult and then marking these signifiers with stress marks before saying these words to a timed beat. This exercise was invaluable for helping me pronounce Greek, Latin or English terms (e.g., the famed Kittel is pronounced Kitt-el/Kit-l, not Kit-tel). In closing, I'll just say that D.A. Carson also has a useful book on accents that can be found at amazon.com