Think necessity – Only look for the information you really need. The fewer rows that you pull in the quicker your query will be.
Keep it simple stupid (KISS) – When you attempt to get fancy with the queries, it can have consequences. Meaning that the queries can take longer and pull unnecessary data. Overcomplicating a query can cause unintended headaches that are avoidable.
Select before a change – Select statement before you change it to a delete or update statement
Measure twice, cut once when restoring a backup – Setup the restore and then go through the screens to verify that you have the correct databases, MDF and LDF selected.
Always make a backup – Before you start troubleshooting an issue ALWAYS make a backup. Even if you do not anticipate making changes, make the backup. For example, when I accidently dropped a table from the database while troubleshooting, anticipated hours of hardship were avoided by backing up the database before I started making changes.