I have a few for Reimi (that I guess could also be applied to other characters)
Consecutive long range attacks:
go to aeos and get in battles where you can 1-hit enemies, wait for them to either come straight at you, or get to where they will attack your allies and sit still and take your time, it can be frusterating hitting 70 and rushing and missing a shot. This mainly applies to pre-emptive strikes, sometimes the enemy will sit still for a little while, but others they will move right away, so wait for them to stop to shoot.
Also works for Bacchus
Interrupt enemies casting:
The trees on lemuris would be a good place for this, they cast a spell probably 33% of their attacks (from what I've observed) and you can take off your weapon and switch to BEAT:B to lower your damage, then just wait for them to start casting and BAM! smack em in the face.
Winning Battles without MP:
Easily done while getting your consecutive long range attacks, just dont use spells, you wont get all of them, but you'll knock out a lot.
Jump Attack only Kills:
Another pretty basic one, set all characters to manual, and head to Aeos, once there, just with the B button and a direction, and shoot, they should all be close to 1-hit kills, easy enough, just time consuming.
Take no damage X times in a row:
Okay, this one is tricky and the name is deceiving, it means when you take a hit and a 0 pops up. The easiest way to do this is to go to lemuris and get in a fight with the trees, 2 or three in one battle it best. Use Taunt, and then quickly use a fainting potion (invincible but cant act) you should easily get up to 50 hits with 5 or 10 seconds to spare.
Also works for Bacchus
Critical Hits in a row:
This one is another pretty basic one, upgrade your critical hit skill as much as you can (level 10 obviously being ideal) then take off your weapon, put your party on manual and blindside blindside blindside! you have to get 7 in one battle in a row, I did this on lemuris when my reimi was level 30 I think.
Win without being targeted / Win without moving:
Very Very easy couple of trophies, just get some solid melee fighters in your party and just set down the controller when the fight starts, I would recommend going to Aeos, where the fight will be short, you don't want to risk an enemy hitting you and screwing it all up.
Also works for Lymle, Faize
Defeat and enemy with a close quarters attack / Defeat an enemy with leg-only attacks:
When reimi is right next to an enemy, press the analouge (cant spell right now, thats why I'm a math major lol) towards them and attack, it should kick them in the air, do it again if needed when they get up.
Close Quaters also works for Lymle
Critical hit from behind:
Very simple, just blindside an enemy and shoot, and its yours. (unless you get unlucky and it doesnt crit. hit, then just do it again.)
Critical Hit on enemies weak spot:
Upgrade Reimi's critical hit skill all the way, and use her when fighting a boss. I got it on shariel I think his name is (the guy on the cardonian mothership). When he uses his symbol to fire the big ray, and brings up his front, shoot him (being in rush mode helps) and pray for a critical hit.
For the stay in rush mode X seconds, get you BEAT:B Stat to 20, then activate rush mode and just let enemies beat on you, I'd say the phantom boss fight on Aeos is a good place to do a few, just save and reload (like Edge's ambush trophy) to get em all