Prophets SAW'S prayers.

When wearing new clothes
Recite:
اللَّهُمَّ لَكَ الْحَمْدُ كَمَا كَسَوْتَنِيهِ أَسْأَلُكَ خَيْرَهُ وَخَيْرَ مَا صُنِعَ لَهُ وَأَعُوذُ مِنْ شَرِّهِ وَشَرِّ مَا صُنِعَ لَهُ
"O Allah, all praise is to You, just as You have dressed me, I seek Your blessings of it and the blessings of what it is made of and I seek protection and Your refuge from all evil and the evil of that which it is made of".

(Mishkat)
Umar (R.A.) stated that Prophet Mohammad (SAW.) said that if a person recites the following dua when dressing in new clothing and gives the old clothing in charity, then Allah will protect him both in this life and the Aakhirah and he will be under Allah's cover (i.e. he will be protected from all calamities and his sins will be hidden).

(Mishkat)
Alternatively recite
الْحَمْدُ لِلَّهِ الَّذِي كَسَانِي مَا أُوَارِي بِهِ عَوْرَتِي وَأَتَجَمَّلُ بِهِ فِي حَيَاتِي
"All praise belongs to Allah who adorned me with clothing by which I cover (hide) my private areas and by which I obtain beauty in my life".
Note: While removing clothing recite "Bismillah" as Satan does not look at the private parts due to this.

(Hisnul Hasin)