Shoot-Look-Shoot or Shoot-Shoot-Look? A lot depends on the capability of your sensors, the speed and envelope of your interceptor, the engagement scenario (range, altitudes, defended area etc) and the performance of the target Tactical Ballistic Missile.
How capable are your BMD sensors? How are they oriented? Do you have a forward deployed sensor capability? These things matter. If you can detect early, you can generally launch early*. And if you can launch early you can attempt a terminal intercept outside of the atmosphere.
How optimized are your interceptors? Acceleration? Altitude? Ability to compensate for errors and discriminate in the end game? This also plays a role in determining Shoot-Look-Shoot vs Shoot-Shoot-Look.
But when all else fails, execute the BRRRRRRT Shot Doctrine!