The correct way to perform Salat al-Istikhara according to the Sunnah is to first make wudu then pray two rakahs of Nafl. After completing the nafl recite the Istikhara dua while keeping your specific matter in mind. I have already explained this in detail including the full Istikhara dua and step-by-step method. So you can check the full guide on this page for complete understanding.
How to perform Salat Al-Istikahra?