1- Good grammar

Example of what not to do: i like ur blog. the choice of colurs is vry interessting but wurks well.

2Good punctuation

Example of what not to do: I really like your blog. I like all the pictures that you have used? How is it in canada!

3Helpful

Example of what not to do: I like your blog.

4No inappropriate questions/comments

Example of what not to do:  What is your social security number?

5–  Re-read comment

Example of what not to do: Hello! My name is John and I really like your blog because it is very interessting and the choice of colurs is very good. Well donie.(typo)