Patience is Key
Veteran difficulty is unforgiving. Rushing will lead to instant death. Take your time, clear areas methodically, and use cover constantly. Peek corners, eliminate threats, and only advance when safe. Expect enemies to have pinpoint accuracy and throw grenades frequently.
Utilize AI Teammates
Your AI teammates, while not always perfect, can draw enemy fire and provide suppressive fire. Use them as a distraction while you flank or move to a better position. Don't rely on them for kills, but leverage their presence to your advantage.
Grenade Management
Enemy grenades are a constant threat on Veteran. Learn to identify the grenade indicator and move immediately. Sometimes, it's better to retreat to a safer position than to try and fight through a grenade barrage. Use your own grenades to clear out enemy clusters.