וישא את עיניו וירא את הנשים - לג:ה
The best way to be careful from forbidden gazing and thoughts is by occupying the mind with divrei Torah. Rav Wolbe writes in Alei Shur that when one thinks in learning, it is a koach that can protect him from seeing pritzus.
In Chayei Sarah, regarding Yitzchak, it says (24:63) “va’yeitzei Yitzchak… vayisa einav vayar v’hinei hagemalim ba’im”. He saw the camels. Regarding Eisav, though, it says in this week’s parsha, (33:5) “vayisah es einav vayar es hanashim v’es hayeladim.” The first thing Eisav saw is the women.
We see from here that to a great extent what one sees goes according to what his mind is occupied with.
Therefore, whenever one is about to go out onto the street, one should prepare divrei Torah to think about. (Often, a concept or kashya to ponder – something about which you can think in depth – can be preferable to chazara from which it can be easier to become distracted).
(From the notes of Reb Matis Feld)