Writing optimal queries requires considering things like using functions properly, avoiding data type mismatches, ensuring join predicates and statistics are defined, and addressing issues like clustered GUIDs. Developers should also avoid anti-patterns like using temp tables unnecessarily, putting filters in HAVING that could go in WHERE, and handling multiple aggregates carefully. The document provides tips for writing efficient queries from Sourabh Agarwal, a Microsoft premier field engineer who blogs and is active on Facebook and Twitter regarding SQL Server topics.