The key to knowing God's purpose for your life is to know God on purpose. Paul, writing to the Romans, says that if your want to know God's purpose for your life make knowing God your purpose. If you do that, He promises that He will reveal His will for you.
Why is it important to know your purpose for living?
If you are not guided by your purpose, you will be misguided by your personal preferences. A purpose gives you something to live for that is bigger than yourself and what you want. A life guided by personal desires never seems to end well.
If you are not guided by your purpose, you will be misguided by your passions. A purpose takes emotions and emotional decision out of play. How many good decisions have you made when you were overcome by your emotions? A purpose begins with the end in mind and chooses or decides based on what accomplishes your purpose.
If you are not guided by your purpose, you will be misguided by your prejudices. A purpose is based on a process and on principles not on personalities or people. A purpose is focused on arriving at a certain result and prioritizes according to whatever accomplishes the purpose rather your petty personal judgments.
Are you living on purpose? Do you have a clear idea of what your life is to accomplish? If so, it is because you have purposed to know your purpose. You have purposely made knowing God your purpose. That purposeful quest has lifted you above your personal preferences, above your passions and above your prejudices.
Know God, know purpose. No God, no purpose.