Several traditions have mentioned the virtue of this night in which it is narrated that Allah turns especially to his servants and accepts their prayers; therefore one should wake up in the night and pray Allah and spend his time in dhirk, dua, tilawah etc. A weak tradition of Ibn Majah mentioned to keep the fast of the next day too; therefore keeping fast of the next day is mustahab. But, there is no proof of wearing new dress.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband