Time Out says
Getting into the Wimbledon Championships at the All England Lawn Tennis Club requires quite a bit of prep. Seats on Centre and Number One courts are distributed by ballot the preceding year, although enthusiasts who queue on the day may gain entry to the outer courts. There are around 500 tickets each for Centre Court (from £56on the opening days) and Courts One (from £45) and Two (from £41), and around 3,000 more for ground admission. You can also turn up later in the day and pay a reasonable rate for seats vacated by spectators who have left early.
Tickets are not sold over the telephone, but on a strictly one per person queueing basis; payment is by cash only. Many turn up with tents in tow the night before to secure their place in 'The Queue'. If you can't face the urban camping, you'll need to turn up long before 9:30am. Don't be tempted by touts or other unauthorised agents, buying from them means you'll be refused entry to the grounds.