Avoid calling methods using strings that can accept methods. This approach will make use of reflection that can slow down your game especially when used in the update function.
Examples:
//Avoid StartCoroutine with method name
this.StartCoroutine("SampleCoroutine");
//Instead use the method directly
this.StartCoroutine(this.SampleCoroutine());
//Avoid send message
var enemy = GameObject.Find("enemy");
enemy.SendMessage("Die");
//Instead make direct call
var enemy = GameObject.Find("enemy") as Enemy;
enemy.Die();