iota subscriptum is not an accent, and I think that at least beginners should write it as adscriptum and pronounce it, in order to avoid confusion, ease the reading and better memorize the terminations/contractions.
As for accents, I suggest you master each accent at a time, the fact that your text book expects you to swallow them (which causes most people to puke, rather than understand them), doesnâ€™t mean you have to learn them all at the same time.
Leave the grav a lone for a moment.
Gain a good control over the acute, and about a week later master the rules for the circumflex. Start with simple words such as dou~los dou'lou.
Remember: nouns and adjective retain the original position of the accent.
The circumflex is only â€œplacedâ€ on one of the last two long syllables. The penult (second syllable from the end of the word) can take a circumflex when its long and the ultima (the last syllable) is short. Hence when the termination becomes long(as in the case of douâ€™lou) it would change to the acute. I remember reading somewhere that the circumflex is actually a combination of of grav and acute - I think it was in an old primer or goodwin.
The grav is the most simple: when you have an acute on the last syllable turn it into grav(except if there's an enclitic, but leave this matter for a later time.)