I always focus on the following to improve my Hubs:
I use the title tuner to get a good title if the current tittle is not ranking well .
I correct all the grammatical and lexical errors
I update the content to make it more relevant
I rewrite the Hub summary ensuring I incorporate the necessary Keywords
I add video and other capsules
I remove capsules that have link to exterior pages portraying the page to search engines as a 'door way page' (Excessive Amazon and Ebay Links)
With these corrections I have achieved significant success with my few Hubs