We numerically and analytically study orthogonal and angled coupling schemes between a dielectric slab waveguide and a plasmonic slot waveguide for a large range of geometric and material parameters. We obtain high orthogonal coupling transmission efficiencies (up to 78% for 2D calculations, and 54% for 3D calculations) over a wide range of refractive indices, and provide simple analytic arguments that explain the underlying trends. The insights obtained point to angled couplers with even higher coupling efficiencies (up to 86% in 2D, and 61% in 3D). We find that angled plasmonic coupling is well suited for large dielectric waveguides at the phase matching angle. These results suggest new capabilities for efficient dielectric-plasmonic interconnects that can be applied to a wide variety of material combinations and geometries.