Concerning trying not look at girls:
Saint Alphonsus Liguori recommended the practice of the three Hail Marys.
Find out about this Devotion and do it in the morning and at night, it is really helpful for Purity.
It can even be done whilst lying on the floor, in utter humility.
We can pray the Rosary to be granted Purity.
Also, we can wear the cord of Saint Philomena.
We can pray to various Saints for Purity.
Particularly, we could pray to Our Lady and to Saint Joseph about this.
Also, we can pray to Saint Philomena and many other Virgins who have been canonized.
We can also have Purity as an intention for some of our Masses.
And we can ask a Priest to say Mass for this intention for us.
We must have an absolute will to avoid the sins of impure thoughts, lust of the eyes, etc.
If we are sincerely determined to avoid these mortal sins, it is easier to gain the graces to avoid them.
The resolution must be absolute on our part.
Among the most difficult sins for men to avoid are the sins of the flesh.
We can meditate on the fact that if we give way to impure thoughts or forbidden glances, we are hurting Our Lord.
If we consider that our impure thoughts may add to the Sufferings Our Lord underwent in the Crowning of Thorns, we may feel too upset, owing to love of Our Lord, to think the evil thoughts.
I am not certain, but possibly I may have read somewhere that there is a connection between sinful thoughts and the Crowning of Thorns.
So this may cause us to feel shame which can stop us.
None of us want to hurt Our Lord.
Also, we must just avoid immodest girls.
It is playing with fire to have anything to do with them.
Girls can be very, very tempting.
We must have an absolute determination not to sin, by looking at them.
We can be punished by God for keeping bad company, by God allowing us to fall.
Saint Francis of Assisi only had an indistinct picture of what some women he gave spiritual direction to, even looked like.
The reason for this is that Saint Francis did not look directly at women, even when he was talking to them.
This is something which really helps in the fight to banish lustful thoughts.
Moral Theologians used to talk about forbidden glances.
We should not even look unnecessarily at women.
If a man does not see what tempts him, the temptation loses its strength.
This was one of the ways by which Saint Francis of Assisi won his Glorious Crown in Heaven.
Saint Francis did not look directly at women even when he was talking to them.
He gave spiritual advice to certain women, but he did not even know exactly what they looked like.
If I recall correctly, I was told that Pope Saint Pius X said that Saint Francis of Assisi was the most Christ like man who ever lived.
Our Lady of Fatima made it known that more souls go to Hell for sins of the flesh than any for other reason.