Ignoring button clicks for second action

Sorry for the title, I didn't know how to word it correctly.

Let's say I have a script:
This script has 2 states.

State 1: Idle
State 2: Unit Selected

State 1: if (left mouse button is clicked) {
Highlight friendly unit
switch to unit selected state
}

State 2: if (left mouse button is clicked) {
move unit to click position
}

Now the problem I'm having is that when I click to select a unit in the first state, the code accepts that click, but will switch states, get the location of the click and spawn the unit all within that same click of the button. Is there a way I can make the code take the first click then wait for the second click to initiate the second state?

I've tried switching the states only on mouse button up, but this does not seem to work.
Here's the actual code if my explanation doesn't make any sense.

 if (currentState == State.Empty) { //NOTHING SELECTED
 
             if (Input.GetMouseButtonDown (0)) { 
 
                 RaycastHit hit;
                 Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 
                 if (Physics.Raycast (ray, out hit, 100.0f)) {
                     Debug.Log ("You selected " + hit.transform.name); 
 
                     //IF PLAYER CLICKS ON A UNIT
                     if (hit.transform.tag == "Unit") { 
                         SelectedUnit = hit.transform.gameObject; 
                             currentState = State.Unit;
                     }
                 }
             }
         }
 
 
                 if (currentState == State.Unit) { //UNIT CURRENTLY SELECTED
 
                 if (Input.GetMouseButtonDown (0)) { 
                 RaycastHit hit;
                 Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
                 SetTilePos ();
 
                 if (Physics.Raycast (ray, out hit, 100.0f)) {
 
                     //SELECT TILE WHILE UNIT IS SELECTED
                     if (hit.transform.tag == "Control") { 
                         SelectedUnit.GetComponent<AIMoveTo> ().target = hit.transform;
                         ClearUnit ();
                         currentState = State.Empty;
                     }
                 }
             }
         }