There is much we don't know about the devil's methods, but we do know we need to be alert and constantly on guard against him, and not let ourselves be led astray by his lies. The Bible's warning is clear: "Be self-controlled and alert. Your enemy the devil prowls around like a roaring lion looking for someone to devour" (1 Peter 5:8).
Yes, at times the devil does seem to put thoughts into our minds at least if we are open to his influence. At one point in Judas' life, we read that "Satan entered into him," and he immediately left to betray Jesus (John 13:27). Judas had already decided to betray Jesus and had already made his arrangements but from that moment on there was no turning back.
But Satan doesn't have to put thoughts in our heads to get us to do wrong, because we already lean that way. Our sinful nature is constantly pulling us away from God, and tempting us to do evil. The Bible says, "But each one is tempted when, by his own evil desire, he is dragged away and enticed" (James 1:14).
The most important thing I can say about this, however, is that Christ has defeated Satan! By His death and resurrection He overpowered all the forces of death and sin and evil, and He helps us overcome Satan's temptations when we turn in faith to Him. Have you committed your life to Him?