Lens-free on-chip digital holographic microscopy (LFOCDHM) is a computational imaging technique whereby the sample is placed directly onto or very close to the digital sensor and illuminated by a partially coherent source located far above it. However, unlike conventional coherent diffraction-limited imaging systems, where the limiting aperture is used to define the system performance, typical lens-free microscopes only produce compromised imaging resolution that are far below the ideal coherent diffraction limit. In this presentation, we analyze 5 major factors that may contribute to this limitation, namely, the sample-to-sensor distance, spatial and temporal coherence of the illumination, finite size of the equally spaced sensor pixels, and finite extent of the image sub-FOV used for the reconstruction. We will also discuss how to build an LFOCDHM system by optimizing these relevant parameters, achieving both high-resolution and wide field-of-view microscopic imaging with a miniaturized platform.