Positive diction has a lot to do with connotation. The connotation is a big part within diction and it can be positive, neutral or negative. The writer uses connotation to display certain emotional meaning to the text; and uses certain types of words and expressions to create more of a positive, neutral or negative reaction to the text depending on his purposes.
I'll give you an example:
If I, as a writer, intended to talk about Duke, my Weimaraner, in a book, I could talk about his behavior in 3 different connotations and for this I would use different words:
As you can see in this case I chose words, more specifically adjectives, because I wanted to give a certain tone and create a certain impression of Duke, on the reader. The first sentence is a perfect example of positive diction.
By the way, Duke is just adorable, I can't think about anything but his lovable long ears. (Yes, I did it again! positive diction).
