Advice about mistakes to avoid

Today in class I told everyone to be careful about the following when they write:

1. Spaces
   You need to have a space after every period (.), comma (,), and after all other punctuation marks. Do not put a space before a period (.) or comma (,).
2. Writing in paragraphs
   Do not start a new line after every sentence.
3. Using the plural form to make general statements
   "I like dogs" is different from "I like a dog."
4. Explaining Japanese things
   "My favorite artist is Ayaka." Who is Ayaka? "My part time job is Yoshinoya." What is Yoshinoya?
5. Understanding my corrections
   I don't expect you to fully understand all of my corrections. You need to ask questions. If I wrote a question mark (?), that means I didn't understand what you wrote and I want to talk with you about it.
6. Making sure your introduction is long enough
   Your introductions need to be more than 150 words. If your introduction is too short, I will tell you so a comment on your blog.