There is no magic formula or definitive test that can tell us exactly what our spiritual gifts are. The Holy Spirit distributes the gifts as He determines (1 Corinthian 12:7-11). A common problem for Christians is the temptation to get so caught up in our spiritual gift that we only seek to serve God in the area in which we feel we have been gifted. That is not how the spiritual gifts work. God calls us to obediently serve Him in all things. He will equip us with whatever gift or gifts we need to accomplish the task He has called us to.
Identifying our spiritual giftedness can be accomplished in various ways. Spiritual gift tests or inventories, while not to be fully relied upon, can definitely help us understand where our gifting might be. Confirmation from others also gives light to our spiritual giftedness. Other people who see us serving the Lord can often identify a spiritual gift in use that we might take for granted or not recognize. Prayer is also important. The one person who knows exactly how we are spiritually gifted is the gift-giver Himself—the Holy Spirit. We can ask God to show us how we are gifted in order to better use our spiritual gifts for His glory.
Yes, God calls some to be teachers and gives them the gift of teaching. God calls some to be servants and blesses them with the gift of helps. However, specifically knowing our spiritual gift does not excuse us from serving God in areas outside our gifting. Is it beneficial to know what spiritual gift(s) God has given us? Of course it is. Is it wrong to focus so much on spiritual gifts that we miss other opportunities to serve God? Yes. If we are dedicated to being used by God, He will equip us with the spiritual gifts we need.