Turn Restrictions for Oneway Streets and Dead Ends

It is not necessary to add turn restrictions on one-way streets. Simply adding the tag oneway=yes will implicitly create all the relevant turn restrictions. It is the responsibility of data consumers (routing software, in this case) to generate turn restrictions if these are required within the application. All software that I am aware of seems to do this successfully.

Obviously there may be exceptional cases (for instance a street crossing a one-way street with straight-on only restrictions), but these can be handled in the normal way by creating turn restrictions.

Roads which are dead-ends again can be detected as such by application software, and there is no need for any explicit tag. However, a tag does exist noexit=yes for this purpose. It is frequently used to tag streets (ways) where a complete survey has not been done, but a no exit sign exists at the entrance to the street.

If it is obvious (no turning to one way street) it not necessary to map it. The easiest way to create turn restrictions is registering in cloudmade.com and using their editor Mapzen. You just click a node and it gives you a small GUI with a car to click where the car can drive - easy, intuitive, fast.
Otherwise it is done with relations and adding the individual streets as roles.