Of course, first and foremost, pray and seek God so you will know your purpose. What do you "notice" often? What makes you cry? What makes you angry? Do you look at a situation and the whole scenario of how YOU would fix it runs through your mind? When you realize those things, you are on your way to knowing your purpose. Meditate on those things and pray. The Holy Spirit will "leap" within you and you will know for certain.
Now that you know your purpose, you have the measuring stick--the tool--to decide whether that "good thing" you are approached to do is in line with your purpose. We need to have tunnel vision with a single minded purpose to effectively run the race placed within us by God.
Recently I was reading about John the Baptist. I can think of no greater example of a man born to fulfill a purpose. A man whose purpose was evident even while he was in his mother's womb. Luke 1:41 When Elizabeth heard Mary’s greeting, the baby leaped in her womb, and Elizabeth was filled with the Holy Spirit. While still in his mother's womb, he announced the presence of Jesus, in His mother's womb!
John the Baptist's purpose was to prepare the people for the coming of Jesus and His message of the Kingdom of Heaven... to announce that the Messiah was coming. He certainly didn't fit into any "religious boxes" of the day. He was unique and single-minded in purpose. When the people heard his message, people repented and he baptized them. They were being prepared for Jesus.
I went on to read about his death and God showed me something in those scriptures I had never noticed before. We can read a scripture many times and then God shows you that same scripture from a different perspective! In Matthew 14, it tells the story of Herod Antipas putting John the Baptist in prison. John the Baptist had angered Herod's "illegal" wife, Herodias, (she had been divorced several times and had been married to his brother, Phillip) by confronting Herod about his sinful marriage. Even though Herod put him in prison, he would not kill John the Baptist for fear of public opinion. Herodias--operating under a Jezebel spirit--contrived a way to force Herod to behead John the Baptist.
When reading Matthew 14 I saw, for the first time, the perspective that even though John the Baptist was speaking the truth and he was doing a good thing, telling Herod that he was in a sinful illegal marriage was not his true purpose. He was called to prepare the people for Jesus' ministry. John the Baptist wasn't put to death for his true purpose. He was murdered because he boldly dared to confront the king about his sinful life. Don't get me wrong, I am not criticizing John the Baptist or his actions. He was passionate and outspoken. He spoke the truth with boldness. Wow...to be that passionate and committed! But when I was reading, God showed me the importance of being single-minded and so "zoned in" on my purpose that I will not even be distracted by a good--or even great--thing!
Find your purpose and be specific. Plant it in your heart and mind. Then always use it as your measuring stick when deciding how you will spend your precious time and energy. Use it in everything you do!