It makes sense to take up the iambic trimeter after studying the dactylic hexameter, for the trimeter is somewhat more complicated, primarily due to the resolution of long (and even short!) into two shorts.  You will recall that the dactylic hexameter allows only contraction of the two shorts into a long.

But let's not get ahead of ourselves.

If you have not studied the material and done all the exercises in §§2-4 on syllabification, short and long syllables, and scansion, and the material in §5 on the dactylic hexameter, I would urge you strongly to do those sections before proceeding with §6 on the iambic trimeter.  In particular §§2-4 are essential, but §5 too should be studied.  The present section builds on those preceding ones, and I assume that you know that material.  You will save yourself much confusion if you make sure you know what's in §§2-5 before continuing here.

The rules you have already learned on syllabification and scansion apply equally for the iambic trimeter, and in fitting lines into this pattern (see next section, §6.2) you proceed as you did before.  One difference is worth noting, and that has to do with the mute [C₁] + liquid/nasal clusters [C₂] (§2.6 and §2.7):  in Homeric poetry, this cluster tends to split in syllabification as C₁-C₂ whereas in the iambic trimeters of tragedy it has an equally strong bias to syllabify as -C₁C₂.  As you know, this difference in syllabification usually makes a great difference in your scansion!

The iambic trimeter is most common in those portions of Greek tragedy (and comedy) that involve rheseis (speeches) and stichomythia (line-by-line dialogue or even line-within-line repartee [ἀντιλαβή]).  We have 33 extant complete tragedies (7 each from Aeschylus and Sophocles and 19 from Euripides) plus numerous fragments from the plays of these three authors as well as many others.  And although those 33 plays represent probably less than 1% of all Athenian tragedy written, most of their 44493 lines of Greek are iambic trimeters.  We thus have a sufficiently large corpus (the Iliad and Odyssey alone give us together 27803 lines of dactylic hexameters) of material for studying what was no doubt the best in tragic iambic trimeters.  The iambic trimeter (and tetrameter) also appears in slightly different forms in other types of ancient Greek verse, notably lyric poetry, but we shall take those up a later point.

If you would like to read a quick and compendious survey of the 'history' of users and usage of the Greek iambic trimeter from the time of Archilochus (7th century BC) up into the medieval period, I could do much worse than to commend Kerkhecker 3-6 for your consideration.

And now it's on to the iambic trimeter of Athenian tragedy.