Based on the level of respect or formality, you can say "Go straight! Then turn left/ right!" in Korean in 3 ways:

• Informal: jjug gaseo oen/oreun jjokeuro ga (쭉 가서 왼/오르쪽으로가.)
• Formal: jjug gaseo oen/oreun jjokeuro gaseyo (쭉 가서 왼/오른쪽으로 가세요.)
• Very formal: jjug gashuseo oen/oreun jjokeuro ga (쭉 가셔서 왼/오른 쪽으로 가십시요.)