When you go to the store and buy a gallon of milk or a big bag of dog food, you don't give the whole gallon to the baby in one sitting and say, "OK, now I have fed the baby for the week!" Nor do you give the whole bag of dog food to the dog, because you know the dog would really try to eat the whole thing at once and get sick! Wisdom knows the better way, and God wants to instill wisdom in us.
Some, when they first get a prophetic urging to prophesy are too "nervous" to give it, so they hold back. Later, others who got past that stage can often be too zealous to not hold back! I have seen people competing in a church service to give a prophetic word. Some were so aggressive that the pastor had to stop allowing them for a season until the people matured.
If you give a word that's not fully correct, pastors and leaders will most likely and should publicly yet kindly correct it, and do so for the sake of the whole Body present who heard that "word." Knowing this keeps people accountable for their words.
The best way to learn your prophesying gift expression is in small groups where it can be judged among those in the group with leadership and with the Word of God. If you feel you have a word that seems strong, it may be better to write it down and submit it. This will give all concerned time to ponder the "word."
It is the devil who says "Hurry! Hurry! Hurry!" God has peace. The Truth will not go away. Just because you fail to give a word does not mean that God's Spirit is not at work with a person, especially if there are other seasoned ministers around, but realize, too, that a prophetic word can strongly determine a person's ability and growth in the Lord and so it is better to fail at giving too much trying to be a blessing rather than too little. (But if you find it is destructive, then it may be best to pull back until you have better understanding.)
Even with "judgment prophecies" God will give space for people to repent--without further help or accountability to the prophet giving the word. The prophet is only the messenger, not the Judge of Accountability. And judgment type words are best left for seasoned ministers to give, as the accountability for the anointing of that word is greater in God.
The Apostle Paul encourages us to prophesy -- according to our faith. Just because we miss it a time or two, we should not despise prophesying. It is one of the better gifts, he says. But we grow in our strength and ability to prophesy by our strength in the knowledge of God's Word and our walk in His Spirit. All may prophesy the Bible says--it is not just for a certain few. Stronger authority may be on the office ministries, but one good word can cheer a heart with much needed encouragement and break a bondage and set a captive free!
God's Rhema word will always be challenged by the devil who comes immediately to steal the Word of God from the believer if he can. Distractions, disturbances, insecurities, lack of knowledge, going on and on too long--all these things can cause the effectiveness of the prophetic word to perish in a person's heart.
We also must remember that prophetic ministry is only one-fifth of the five-fold ministry of God. We must have the balance of the other four fold ministries in our lives. We need teaching, pastoral nurturing, to be evangelized back to our first love and to be evangelists ourselves, and we also need to be established in different areas of our lives in God. Anything not in balance will tumble and fall when the shaking comes and it will come. God works in balance more than He does in lopsided exertions, for pride comes before a fall, and this can easily happen with the zeal that comes from newly released spiritual gifts.
To everything there is a season and a time for every purpose under Heaven--there is a time to keep silence, and a time to speak, as it says in Ecclesiastes 3:7. Holding back can be just as wrong as speaking out! So many with prophetic gifts are not certain if what they have is from God or not--but the only way you are going to know is to test it! Find a good covering (if you don't already have it) and be willing to be corrected and accountable. You will most likely then find your spiritual gifts manifesting and thriving and thus enriching the Body of Christ.