Hi Munb
Your first port of call is to find a REPUTABLE breeder who breeds for the ring.I suggets you go to some champ shows and watch the dobes and see what ones you like.Look in the catalogue and see who bred them and get talking to some people round the ring.
If you buy from someone who does not show you are VERY unlikely to get a show quality pup...even if they say there is x amount of champions in the pedigree etc. A good breeder will only want to see good examples representing their affix in the ring.
Secondly you need to find a ring craft class to help train you and your pup how to show.Your breeder will also be able to offer you help and advice re show preperation.
next you need to find some shows ...
http://www.prodogs.co.uk and send in entries once the pup is old enough.A pup must be 6 months to start showing.
Good luck...it may sound a lot of hard work but its fun and well worth the effort
Archer