Have generals meet secretly in an important cultural site so the US can't bomb it even if it finds out where they are under the Geneva Convention. Send orders by paper so the US can't read them in advance.
Have the armed forces fight like the IRA did in 1917-1922. Kill soldiers, officers, spies, any snitches, and harass the USA until it gives up and goes home. Have the subs torpedo US ships if they can get away with it. Send assassins under false passports to the US to kill Congressmen, Senators, generals if they can.