If a database has a table of session one can try to steal cookies or other credentials from the table to authenticate as another user.
If one is in a database with write access and there are roles assigned to users, give the current user admin rights.
SQL Injection Cheat Sheets
Universal Structures
information_schema Metadata and all the databases and tables
information_schema.schemata Databases
information_schema.tables Tables
information_schema.columns Columns
sqlmap
GET
Discover vulnerabilities in databases as well as dump info
sqlmap -u <URL> --batch
POST
# With request file
# Add request into a log file (either from Burp or Chrome)
sqlmap -r <request_file> --batch
sqlmap -u <URL> --data "username=*&password=*"