Hi imReana!

First of all, you should get a Remote Control. This will help you train: no need to manually click skills or monsters. You can just auto attack, auto move, and auto heal if you have food.

If you don't know how to get a remote control, just follow this steps:
1. Go to Welling Village

2. After you get there, do this quest:

Auntie's Special Soup Ingredients

Target: Aunt near the Weaponry of Welling Village

Condition: None

Process: An aunt cooking soup finds out her ingredients have been used up. She asks you to take the potatos from the Fruit Grower at once.

Note: The Fruit Grower is just in the village. You can find him near the entrance.

Reward: Remote Control*1

Then you can follow Lord Death's suggestions. You can train in kelan cave and you can leave your chars AFK if you have the remote control.