Visa officers have hundreds of applications to look over and only have a few minutes to decide on your file. So keep your SOP as short as possible. Write the SOP in a natural language without any deliberate complexity.
In terms of your refusal, simply address the concerns of previous VO for the reasons they provided. For instance, if they think that you don’t have a clear purpose of visit then structure your SOP in a way that will clarify to the VO that your intent is to temporarily study in Canada.
Good luck.