it depends on the context or what do you want to say

"by this way" is not used. You can say thus : 1. I can teach you my language and you can help me learn yours and THIS WAY, my language will improve along with yours. 2. In this sentence, the author speaks in detail about the problems human beings face. BY THIS, he wants to communicate that we need to be more helpful and tolerant as human beings. 3. Gautam Buddha traveled far and wide and taught the world that the cause of sadness was desire. He taught the people to be kind, helpful and better human beings. IN THIS WAY, he made the world a better place to live in.

You would not say "by this way". You would say "by this"(rare), "this way"(common) or "in this way"(also common).