One way to guarantee entry into a Real Madrid game is to buy it as part of a package. Viator.com offers two nights' stay in a three-star hotel and entry into the game of your choice. You pay a more than if you bought the ticket and hotel separately, but at least there is no chance of the tickets selling out.
Guided Tour of Madrid with Visit to Santiago Bernabeu (Buy Direct).
Guided tours of the stadium are free with the Madrid Card.
