Just revisiting some questions raised...

But these days, my teacher asks for demonstrating to me proactively how to set a pen on the paper when painting from life or literary sketch. At that time I understood, indicating a direction timely is based...

But these days, my teacher asks for demonstrating actively demonstrates to me proactively how to set a pen on the paper when painting from life or literary making quick sketches. At that time I understood, indicating a direction timely with a flash of inspiration/insight ...

is based on our insist on going straight forward just requires us to draw with confidence and certainly

shangyu 22 minutes ago: Thanks a lot, sir. I want to express:

"主动地“ by "proactively"  (try 'actively' instead)
"写生" by "painting from life" (are you using a brush or a pen?) drawing from life since you are sketching - 写 also means 'draw'

"速写" by "literary sketch". (literary sketch is a written work ) 速 has the speed meaning

"indicating a direction timely", I want to express a meaning similar to "点化", having a little bit sense of satori in Buddist. Thanks again

Proactively means something like 'taking action anticipating events' as opposed to 'reacting to events' -it is not appropriate here, although your Chinese 主动地 translates as 'proactive'

literary sketch, short prose narrative, often an entertaining account of some aspect of a culture written by someone within that culture for readers outside of it

Satori (悟り?) (Chinese: 悟; pinyin: wù; Korean: 오 o; Vietnamese: ngộ) is a Japanese Buddhist term for awakening, "comprehension; understanding".[web 1] It is derived from the verb satoru.[1]

In the Zen Buddhist tradition, satori refers to the experience of kenshō,[2] "seeing into one's true nature". Ken means "seeing," shō means "nature" or "essence."[2]

Satori and kenshō are commonly translated as enlightenment, a word that is also used to translate bodhi, prajna and buddhahood

sketch class/drawing class (was it sketch or drawing - the difference being that 'sketch' is for rapid and unfinished drawing)

Yesterday I went to take a sketch class in sketching. My The sketch teacher is a young man, and it is his he has a habit of not casting even a glance at me, and says almost saying nothing about my work before until I have completed the my whole drawing. Even if I want to give up my job  not knowing how to use the lines to shape plastic effect on my paper, he only tells me YOU CAN DO IT.
But these days, Recently, however, my teacher asks for has started demonstrating to me proactively(?) (I think that's the wrong word, 用中文怎么写？）how to set the pen on the paper when painting drawing from life or literary(?) (I think that's the wrong word, 用中文怎么写？） sketch. At that time Then I finally understood, indicating a direction timely is based on our insist determination on going to proceed directly straight forward, (I half understand your meaning, but not quite) which no one else can do for anyone cannot take place of us.

sketch

Yesterday I took a sketch class. My sketch teacher is a young man. He has a habit of never casting a glance at me and almost saying nothing about my work before I complete my whole drawing. Even if I want to give up my job when I don't know how to use the lines to shape plastic effect on my paper, he only tells me YOU CAN DO IT.
But these days, my teacher asks to proactivly demonstrare how to set a pen on the paper when painting from life or literary sketch. At that time I understood, indicating a direction timely is based on our insist on going straight forward which anyone cannot take place of us. (this last line is a bit mixed up, what message are you trying to get across?)

very good job! keep up the practice!