Choosing a Title

A good title can make a vast difference to book sales. In general the best titles for fiction are short - five words or less. At the time of writing the top 20 fiction books at amazon have an average of 2.3 words and 14.2 characters. Three of the top 20 fiction books I checked had titles consisting of a single word. The longest were 4 words. 

Titles in non-fiction tend to be longer. The top 20 non-fiction books I checked had titles averaging  3.2 words  and 19 characters. The longest of these was eight words.

According to Amazon you don't need to use keywords in the title or use the title as a keyword because Amazon already uses titles as keywords when a search is made. 

Does your book need a subtitle?

Subtitles tend to be longer, especially in non-fiction. Of the top 20 fiction titles I checked two had no subtitle and for two the subtitle was simply 'A novel' Average length of subtitles for fiction was 34 words. In non-fiction the average length of subtitles was 48 words. Two of these non-fiction books had no subtitle

In these examples of a top twenty books the subtitle is shown after the colon in the title. 

Subtitles are a good place to use keywords, 'Stuff words' and  'Power Words'.

Power Words

There are hundreds of words which trigger an emotional impact on the reader making something more likely to catch their attention. An expert writer of headlines is well aware of these but this isn't true of many authors. Use 'power words' in your titles, subtitles and book descriptions if you can. They will help your book sell.

I've produced a list of some power words here. I don't profess to know all of them. To help you, I've also attempted to put them into the emotional categories you want to trigger - Adventure; Anger; Curiosity; Envy; Fear; Greed; Lust; Romance; Sloth; Trust; Vanity.