Although weapon mastery slows down once you get to the 700+ level, it can go into a halt at 900+ when you are not mastering your weapons efficiently. In this section we will discuss some common ways for you to master your weapons faster.

When you have higher weapon mastery, your hit rate is improved with the chosen weapon. A good level to still master your weapon of choice is around 115~120+.

Do not bring a partner when you are weapon mastery grinding because you want to drag out the battles.

Important Pointers

1. Use a low DPS weapon.
Your goal is to drag out the battles without healing often. This means that you can consider equipping a shield with a 1 handed weapon to quickly

2. Auto attack
Auto attack can land the most numbers of hits under the shortest period of time.

3. Attack Speed Skill Buffs
1. Effect booster (enhances duration of buffs)
2. Speed Master (10% reduction in attack interval)
3. Brave storm (10% reduction in attack interval)
4. Star Saber (10% reduction in attack interval)
5. Sword Dancer (5% reduction in attack interval)
6. Stealth POS (5% reduction in attack interval)
7. Speed Stance (passive skill 5% reduction in attack interval)
8. Double attacks

You can consider using attack interval reduction items as well.

4. Useful Gears
Some useful equipment that can improve efficiency of your weapon mastery grind can be under the following categories:

a. Weapon interval reduction.
Any that reduces weapon interval (e.g. Mirage belt)

b. Survival gears
This category include ones that either improve your dodge or your HP regen. If you can manage to gear enough to take hits AFK without dying, you can even leave your vita on all night long while skilling the weapon mastery automatically.

c. Optional equipment
Hit+ gears during early stages of weapon skill mastery if you missed alot.
Any necro coat to reduce cooldown of effect booster)

5. DLC Mission + Implement “Additional Sale of D Value Impact Gear” NOT cleared.
With the implement active, you get -50% attack interval and a certain amount of double attack and hit +50. So you only need to make up an additional 50% through skills and equipment to cap.

The buffs you receive during that implement is only available while the hollow mission is active. The DLC mission has a 240 min duration!

6. Mob selection
The best mobs are the ones that your character and gears can effectively tank while being able to auto attack them to death.

Reference: http://www.gamefaqs.com/boards/734608-sword-art-online-hollow-fragment/69811939
http://www.critdmg.com/post/93256474724/weaponskilltest