Adjusting Apache Solr bias based on content length?
Under bias setting you should be able to reduce the priority of the fields. So reduce the priority of the fields that is not much important, and increase the priority of the fields that you would prefer for solar to prioritize.

The settings can be found on: admin/config/search/apachesolr/settings/solr/bias

0.1 is the lowest and 21.0 is the highest rating.