ISTJ People of this type tend to be: cautious, conservative, and quiet; literal, realistic, and practical; careful and precise; logical, honest, and matter of fact; resistant to change and comfortable with routine; hard working and responsible. The most important thing to ISTJs is being of service, working hard, and being responsible.
How to Spot ISTJs: quiet, careful, and private
cautious, focused, and hardworking
serious, meticulous, and very literal
neat, conservative, modest dressers
Tips for Communicating with ISTJs: Be prepared and present ideas sequentially
Give them plenty of time to adapt to changes
Stress the practical benefits
(From PersonalityType.com)