Over the years, I've found the FRA airport to be particularly challenging in obtaining VAT refunds and clear instructions are impossible to find.
Below are the steps to obtain VAT (tax free) refunds in FRA Terminal-2 valid on 7 Dec 2014. (Terminal-1 will be different.) Our experience with FRA is that the locations of the export control offices change to in order to make it difficult to execute the steps properly and not all of the airport employees understand the complete procedures.
Items can be placed in carry-on and/or checked luggage.
PART A:: Obtain boarding pass and get luggage tagged to your destination.
PART B:: If there are items in checked luggage, do not leave the suitcase with the airline agent, but take it to the customs/export control station located near the west end of hall-D (on the 'outside' wall). The agents will stamp your VAT form for items in the luggage, take your suitcase, and send it to the plane. Finished with this step, you can go through passport control.
PART C:: For carry-on items, proceed through passport control. The customs/export control office is immediately on the right. The agents will stamp your VAT forms for the carry-on items.
PART D:: obtaining refunds. There are two refund companies now - Global Blue and Premier Tax Free. You must take the forms to the respective companies. Global Blue was located beside the customs/export control office. Global Blue did not charge a service fee if the funds are deposited to your credit card. Premier Tax Free was located beside the entrance for gates D1-4.
-- good luck --