In the heat of the spiritual battle there is a lot clashing of swords, shields, spears, and other armor in the fight between St. Michael and his angels defending us against the dragon and his angels. (Rev. 12:7) Sometimes the good guys get wounded in the tussle and scuffle.
Concerning deliverance prayers, the good news is that if you follow the deliverance prayer guidelines set up in Fr. Chad’s book, “Deliverance Prayers: For Use by the Laity,” (Order here) you can pray for yourself, parents can pray for their children, children for their parents, spouses for each other, and siblings for one another, and you, “will experience little to no retaliation, as a general rule.” (Fr. Chad Ripperger pg.8)
It is when a layperson prays for someone over whom they have no authority, such as a friend, neighbor or parishioner, that they can experience that person’s cross and receive “the flaming darts of the evil one” Eph. 6:16). The word that best describes this occurrence is a “transference,” and St. Faustina gives an example in her diary,
“In a moment my soul became like a stone – dried up, filled with torment, and disquiet…Distrust and despair invaded my heart. This is the condition of the poor people, which I have taken upon myself. At first, I was very much frightened…” 
During a transference, God will allow the person praying deliverance prayers to carry the afflicted person’s cross [despair, pride, desolation, addiction, anger, confusion, deceit, etc.] so that the victim can receive healing graces while the cross [mockery, self-destruction, unbelief, abuse, etc.] is off their shoulders. It is a mystery like when St. Paul says, “Bear one another’s burdens, and so fulfill the law of Christ.” (Gal.6:2)
Another example is when Simon of Cyrene helped Jesus carry his cross or when Jesus asks the apostles three times, “Could you not watch with me for one hour,” (Matt.26:40) in the garden while he spiritually takes on all our sins in the garden. (Yes, at the garden all our sins are transferred to Jesus, “God made him who had no sin to be sin for us” 2Cor.5:21). St. Faustina describes a very rare (almost unheard of), transference, but nonetheless, it gets the point across,
“I saw a servant of God in the immediate danger of committing a mortal sin. I started to beg God to deign to send down upon me all the torments…I felt a crown of thorns on my head…This lasted for three hours; the servant of God was set free from this sin, and his soul was strengthened by a special grace of God.” 
Please note that we never, ever under any circumstances ask to carry their cross [jealousy, self-pity, blasphemy, nervousness, resentment, violence, etc.] as this is only for great saints, victim souls, and mystics. Transferences hardly ever manifest like the example above with the crown of thorns but always at the level of emotional afflicted suffering as Mother Nadine of the Intercessors of the Lambs describes,
“There are many ways that we can experience being a victim of our own intercession. One way is called transferences…Once the person receives the grace the transference will lift…These transferences are usually emotional transferences.” (The Charism of Intercession, pg. 74)
Transferences happen without us asking for them even if you are clergy (bishop, priest, and deacon) and have the power and protection of Sacrament of Holy Orders. I still remember praying for an afflicted person over a decade ago, and receiving a transference. I prayed deliverance prayers for a drug addict because he was struggling, and for an entire day I had the strong desire for drugs. This happened so that the person could experience the cross coming off his back and so that he could receive healing graces for combating addiction. The good news is that transferences are rare if you follow the guidelines.
Fr. Chad explains that a layperson can effectively pray deliverance prayers for a stranger without retaliation if they change the words in the deliverance prayers in his book from, “I command the spirit of ___ …[to] Jesus, I ask Thee to bind the spirit of ___)” St. Faustina shares a better example of what an emotional transference really looks like,
“Once, I took upon myself a terrible temptation which one of our students in the house at Warsaw was going through. It was the temptation of suicide. For seven days I suffered; and after the seven days Jesus granted her the grace which was being asked, and then my suffering also ceased.” 
To prevent a transference, put on the “Armor of God” before beginning by praying Ephesians chapter 6 and remember to always close the deliverance prayers with the “Prayer Against Retaliation” found in Fr. Chad’s book or by praying the, “Cleansing Prayer for the Deliverance Minister,” found in Francis McNutt’s book called “Deliverance from Evil Spirits” [Order here]
These transferences as a rule of thumb do not last long, and the best way to get rid of them is to literally walk them to the cross as this unique book teaches [Order here] or by praying deliverance prayers for oneself during a Holy Hour. Keep in mind that lay people never “lay hands” upon someone’s head in the form of an ordination as this can cause transferences.
You should be a person of profound prayer and in grace to pray deliverance prayers for strangers. Furthermore, to do this work you have to have a deep love for God’s lambs and be willing to “stand at the breach,” (Ps. 106:23) as St. Paul explains this great mystery,
“Now I rejoice in my sufferings for your sake, and in my flesh I complete what is lacking in Christ’s afflictions for the sake of his body, that is, the church.” (Col. 1:24)
Finally, with deliverance prayers there are always exceptions since, “the Spirit blows where It wills,” (Jn.3:8) as when St. Catherine of Siena (third order lay consecrated virgin) liberated the possessed when exorcists of her time ran into a dead end. I have personally seen holy lay people at the John Paul II Healing Center be “the repairer[s] of the breach,” (Is.58:12) when delivering people, or as the gospel describes other lay people casting out demons,
“Then John said in reply, “Master, we saw someone casting out demons in your name and we tried to prevent him because he does not follow in our company.” Jesus said to him, “Do not prevent him, for whoever is not against you is for you.” (Lk. 9:49-50)