Hi Seong Eun, 

It's great that you recognize the importance of self-improvement and are taking steps to work on it, even if you sometimes struggle to stick with it long-term. Remember, everyone has setbacks, and it's all part of the journey. Making commitments like signing up for classes or promising others can be helpful in staying on track. Keep up the effort, and don't be too hard on yourself! 

~Teacher Cathy 

Self-improvement is some effort that you take to become a better person.  

>>CORRECT 

OR>>Self-improvement is the effort you take to become a better person. 

It can be developing skills, knowledge or personality.  

>>CORRECT 

OR>>It can involve developing skills, knowledge, or personality. 

In my case, I don't do something continously in most time.  

>>In my case, I don't do something continuously most of the time. 

Every tries for self developing end in 2months.  

>>Every attempt at self-development ends in 2 months. 

For example, I quit learning Germany in 50days, I quit exercising in a month, I quit meditation in 2weeks and so on.  

>>For example, I quit learning German in 50 days, I quit exercising in a month, I quit meditation in 2 weeks, and so on. 

So I sign up for some class or promise with others to do something continuously. 

>>So I sign up for some classes or make a promise to others to do something continuously.