Basically, hub scores tend to rise if you've written a quality hub on an original topic. Points to remember:
A good title and photograph will increase traffic which raises the score.
Make sure hub is at least 500 words long unless it's poetry. Longer hubs of 1000 to 1500 words (as long as they're pertinent) tend to get higher scores.
Be sure to carefully proof-read the hub before publishing.
Make sure all photographs and graphics are properly attributed and legal to use.
Take time to carefully arrange and enhance photographs so that the hub is visually appealing.
Always answer comments left by others. It encourages them to read more of your hubs and also raises the score of the current hub by adding fresh content.