The paper is organised as follows. We first describe the simulation and analysis methods in section 2. We then show that molecular orientation of anisotropic fluid particles with both repulsive and attractive interactions at the solid and vapour interface of an isotropic fluid cannot generally be predicted using a previously proposed metric, and propose a semi-empirical meanfield estimate of the free-energy difference between the perfectly face-on and side-on orientations as an alternative. We use simulations of purely repulsive particles confined between a solid and vapour interface to obtain quasi-universal relationships for the scaling of the entropic component of the free energy with the shape anisotropy and bulk density of the fluid particles (section 3.1). Combining this estimate of the entropy with an estimate of the energetic component of the free energy from nearestneighbour pair interactions (section 3.2), we show that this free energy parameter accurately predicts molecular orientation at the solid (section 3.3.1) and vapour (section 3.3.2) interfaces. In section 3.4 we generalise these results into a number of practical design principles for OSCs, with the goal of providing guidelines towards rational design of OSC interfaces.