I will only include the irritating and long Achievements. All of the Achievements are fairly easy to do.
Objective: Completed all of the battles in the main and side stories on Chaotic difficulty.
How to make it easier: Even though it takes some time. You probably need to start saving Growth Points, Crystals and Gems for Orochi X. Getting him to level 100 with a 5 star weapon. Also adding the Absorbtion addon to your weapon will make you completely unkillable!
Objective: Obtained an S rating in all of the battles in the main and side stories.
How to make it easier: Same as the last one, just takes some time. I would reccomend the same method. Just to make it faster.
Objective: Completed all of the battle objectives in the main and side stories.
How to make it easier: All of the battle objectives are easy, except the "Kill 700 enemies with any Magic". Some maps don't have a lot of enemies so you have to just use magic most of the time. I reccomend using Nehza (Human) using his Charge Magic Attack does a big amount of damage. Also you can you the Divinity Attribute to help you through it.
Objective: Unlocked all of the Camp Rewards.
How to make it easier: Just focus on getting Orochi X. The Orochi X purchase spot.