Particle Effects Script

How would I got about writing a script which would play a particle effect of a blood splatter when my bullet prefab hits something with a tag called enemy and plays an explosion particle effect if it hits something without a tag called enemy?

In a script attached to your bullet prefab in OnCollisionEnter() check the tag of the object you hit to spawn the appropriate effect.

void OnCollisionEnter(Collision collision)
{
     if(collision.gameObject.CompareTag("enemy"))
          // trigger the blood splatter effect
     else
          // trigger the explosion effect
}

For creating the effects, I’d start with the Unity Particle System.