How ISTPs can develop
The development of personality occurs in phases throughout life. For someone who is young, the main task is to develop use of their preferred mental functions. As one matures, however, and approaches midlife, there is often a need to develop greater comfort with using your non-preferences. This can help you increase your performance at work, and increase your ability to deal with different people and circumstances.
As with all types, an ISTP can achieve personal growth by developing all functions that are not fully developed, through actions such as taking time to consider the impact of the ISTP's approach and ideas on people's feelings, or expressing appreciation towards others. You may need to learn to consult others, and to engender wider ownership of the solution. You may also need to acknowledge and develop your own emotions and personal values, develop a long term personal strategy, and look at personal or networking relationships as having value in themselves, rather than just focusing on collaborative relationships that work towards a particular goal.
A common theme of development for all types after midlife is individuation. This involves learning to value and develop various "opposites", not just the opposite typological preferences. Through reconciling opposites, your personality becomes more individual and unique, and your personality type may change. You might also reach the stage where your closest personality type is no longer a description of you, but it is merely a part of your personal history.
Next: ISTP and Stress