Blessings have been mostly lost to Western Christians. They are used a little in the liturgical churches, but that's about it. Blessings are quite powerful.
What are blessings? The best example is called the Aaronic Blessing. It is in Numbers 6:22-26. "And the Lord spoke to Moses, saying: 'Speak to Aaron and his sons, saying, 'This is the way you shall bless the children of Israel. Say to them: 'The Lord bless you and keep you; The Lord make His face to shine upon you and be gracious to you; The Lord lift up His countenance upon you and give you peace.'''" The apostle Paul had a shortened version of the priestly blessing that he used to bless the believers in the churches. "Grace to you and peace from God our Father and the Lord Jesus Christ." (Eph. 1:2)
Note that blessing isn't petitioning in prayer. It is proclamation, speaking forth of the good you desire. Rebekah was blessed by her brother and it came to pass. (Gen. 24:60) Ruth was blessed by the elders and it came to pass. (Ruth 4:11) Jacob was blessed by his father Isaac and it came to pass. (Gen. 27:27-29) (Gen. 28:3-4)
Blessing isn't prophesying, even though it can be done by a prophet. Prophecies are God's expressing Himself through someone. In blessing, you are exercising your authority as a believer. An example of prophecy is what Esau got from Isaac. (Gen. 27:39-40)
Blessing isn't positive confession. We can't make something happen by our words; we don't have God's sovereignty. We are held in account for our idle words, but we can't accidentally override God. God gives us lots of conditional power of attorney, but He can withhold it any time He wants. In fact, He can override our tongue to get His will done. (Prov. 16:9) The man of God, Balaam, couldn't curse what God had blessed; his tongue was stopped. (Num. 22:4-13)
As Christians, we are called to bless, that we may inherit a blessing. (1 Pet. 3:9) In Luke 6:27,28 says, "But I say to you that hear love your enemies ,do good to those who hate you, bless those who curse you, pray for those abuse you." (Psalm 109:28) Jesus exemplified blessing others when He blessed the children who came to Him. (Matt.19:13)
It would be exceptional if God were to explicitly call you to curse someone or something. But under that circumstance, you would only be an agent of God. You yourself would not be judging.
Part of our blessing will be the loosing of prior curses by ourselves and others. (Matt.23:29-32) The curses that aren't broken remain in effect, just like blessings. The curses need to be broken in general and in detail.
books on blessing: