You can learn more about ways to customize the network from the VisNetwork Documentation or Katya Ognyanova’s phenomal R visualization tutorial.
Also, to improve these results, consider the following changes:
Removing peripheral nodes (i.e. not connected to the largest component)
Remove Retweets (verb == “share”). Note that non-Retweets are verb == “post”. This is the formal definition from Twitter/Gnip of a Retweet, and can be slightly different than simply using “RT” in the body of the tweet.
Color the nodes based on a categorical lable (e.g. Retweets = red, Tweets = blue).
Add in a section that displays the nodes with the highest connections (in/out degree)