Help Replacing 'where Not Exists' In A Query

I am trying to clean up an ugly query that's based on trying to find items that exist in one table but not the other.

My tables are like this:

ITEMS
itemID,
itemName,
itemDescription
etc...

ORDERITEMS
OrderLineID,
OrderID,
itemID

ORDERS
OrderID,
OrderCompleted

Currently my query looks something like this:

Select Items.* from ITEMS where not exists (select 1 from ORDERITEMS inner join ORDERS on ORDERITEMS.OrderID = ORDERS.OrderID where ORDERITEMS.itemID=ITEMS.itemID and (ORDERS.OrderCompleted=1))

So this query is looking for ITEMS what don't have a corresponding entry in the ORDERITEMS table.  As I understand it this is pretty inefficient as it is going to be executing the sub query in the Not Exists statement for each entry in the ITEMS table.  Is the preferred method to do something along the lines of somehow making the sub query into a derived table and doing a left or right join?

Thanks for reading!

Ryan