I am not primarily an advent player, but what i'll say regarding techs is that you should focus first on rushing military prototypes so that you can get defense vessels, drone hosts, or illuminators if need be.
The fundamental of target priority is to limit the amount of damage your opponent can do to you while you destroy his fleet.
This almost always results in a "take out the weak ones first" strategy, and, indeed, this turns out to be the idea in sins.
In general, shoot range frigates (including the illuminator) first, then light assault ships, and then others like capitols/anti-fighter frigs/ etc, heavy cruisers, and finally planetary defenses like turrets (of course if you want to allocate damage on a repair bay or a frigate facts that's your call... and the worthiness of the tactic is dependent upon the sizes of the fleets involved in the battle).
This above "priority" is based upon the general case where range ships do a lot of damage but are the easiest to kill.
Conversely, applying ship types to the equation complicates matters.
Each ship type has its own unique target priority.
For example:
Light assault priority: anti-fighter!, other heavy armor, long range, other light assault, caps, heavy cruisers, etc.
anti-fighter priority: long range! fighters, construction frigates
Note: These things do almost no damage to anything other than these.
Long range priority: long range! light assault, Cap ships, anti-fighter, heavy cruisers, everything else.
Note: Target priority changes due to the "target the biggest threat" notion in a few specific cases.
One example case is when light assault ships threaten your anti-fighter ships, have your long range ships hit them first before targeting your opponents long range ships with your own.
NOTE: Always target planetary defenses last and ALWAYS focus fire (you should even use focus fire with ships with multiple arc firing (like flaks and illuminators), but obviously this is secondary to maneuvering these ships into the center of the enemy line).
Regarding focus fire:
Try not to "overkill" ships. Minimize this as much as possible by targeting a new ship as your "missiles etc" move on to destroy the first ship.
To the poster:
DreamMystic, your diciples are light assault, and your defense vessles are "anti fighter". Your illuminators are long range ships.
Regarding the advent illuminator:
These ships are generally thought to be inferior to other ship types because their damage is split between 3 arcs of fire. I do not believe this to be the case, however, this is only made up for by allowing the illuminator to fire all 3 of its arcs at once. To do this, RAM all of your illuminators (literally) into the enemy fleet. At very close range, all of its arcs will be able to fire at the same group of ships.
Another note: Hitting support ships is a situational target priority. If your opponent only has one guardian, then kill it first. If they have 5 or so however, it may not be worth it to target them at all. It's your call. Support ships are a tricky business.
Another example: targeting hoshiko repair cruisers is a good when your opponent only has 1 or two, however, when they can "repair" eachother this is not worth it. The best tactic with support cruisers is generally to "ignore" them and let them run out of antimatter.
Focus on the weak ships first (or the ones weakest against the ship types you have in your fleet).
Use the reference sheet located here:
http://spreadsheets.google.com/pub?key=p7xc_snd9Cc-6o2UwvPEWUg&gid=1
~Arcturus
