I would first have a think about what type of gsd you would like...
ie longcoat, shortcoat, black/tan, coloured, sable, germanic, english, working line, show line etc - do your research online finding out about characteristics etc and then once you have an idea you can find out what breeders breed the type you prefer.
Once you have found a breeder/s - ask for advice on pedigrees as to what is in there, you can use the health checker on the kc website to look into the hip and elbow scores and inbreeding % - and make a note of these on possible puppy pedigrees. If you are not happy with what you see - ie over breed average (18) uneven (difference of more then 5 between the hip scores) not many generations scored etc.
Then you can rule out breeders/lines you are not too keen on from this information.
When you have the pedigree's that you feel comfortable ask someone to look at them for you.
You could ask pam (wildmoor) on here, Chris hazell (breed health co-ordinator) or Dorothy Cullum (gsd info group/cermar gsd)
They will help you weigh up the risks of what the pedigree may or may not contain....