Use lightweight, sheer interfacings like silk organza or fine muslin to avoid added bulk. Secure with dot adhesive or spray adhesive rather than crisp glues to maintain drape. Reinforce stress points with stay tape or bias-cut fabric strips where extra support is needed.
With practice, you’ll learn the ideal amount of interfacing to provide structure while remaining invisible. Vary the interfacing weight and application technique based on the fashion fabric and desired result.