Late winter is a fairly safe bet for pruning roses. There are shrub roses, rambling roses, climbing roses, groundcover roses, miniature roses, tea and floribunda roses. The rose aficionado will no doubt be more exacting in their timing but I am not a specialist. 

 Standard advice for all rose pruning is to cut to just above a bud. I aim for a shapely shape overall but that's a moot point from rose to rose, particularly ones that are already tangled and overgrown. I note that the RHS advises: "Cut to the appropriate height, if a dormant bud isn't visible" which is basically saying cut to whatever height you think best! 

 Certainly an open shape with some 'air' is preferable in the case of a shrubby rose. Then again a climbing, rambling or groundcover rose is by nature a spreading shape. Cutting out dead and diseased stems, crossing and spindly stems and suckers at the base generally encourages vigour whatever the rose.