How to create SQL index for a faster join?

How to create SQL index for a faster join?

I have the following query without where clause for getting a list of all
Employees and their Orders:
SELECT LastName, FirstName, OrderID, OrderDate
FROM Employees inner JOIN Orders
ON Employees.ID = Order.EmployeeID
I can define two indexes: 1) on column Employees.ID and 2) on column
Order.EmployeeID. If I want to have only one index, which one should I
define for a faster join?
I am using SQLite for Android