Since the realization that we are living in an expanding universe about a hundred years ago, cosmologistshave come quite a long way in understanding our universe. The ΛCDM model, which explains the accelerating expansion of our universe with a cosmological constant, has been shown to be quite robust with observations from three dark energy probes: Type Ia supernovae (SNe Ia), Baryon Acoustic Oscillations (BAO), and the Cosmic Microwave Background (CMB). However, recent results from the past year are starting to create a crack in the once-robust ΛCDM model, showing preference for a time-evolving dark energy. Combined with the fact that the nature of dark energy is still completely unknown, it will be extremely exciting to see results from next generation experiments that will help uncover current mysteries. As we push for sub-percent precision cosmology, we need to improve the measurement pipeline in every way possible, such as by exploiting information that was not used before, or considering effects that were subdominant for past surveys. For my graduate work, I improved the flux measurements of SNe Ia by accounting for wavelength-dependent atmospheric effects as well as provided a methodology to use Differential Chromatic Refraction in our own atmosphere to measure SN Ia redshifts; both flux and redshift measurements are crucial for SN Ia cosmology. For BAO, I investigated the stability of the BAO standard ruler scales under modified gravity and eigen-decomposed the BAO two-point-correlation-function covariance matrix to provide an efficient way of measuring errors on the BAO scales; these works pave the way for a more model-independent and efficient BAO cosmological analysis. Additionally, I quantified the change in the Cosmic Infrared Background (CIB) non-Gaussian statistics due to weak gravitational lensing, which will be valuable for next-generation surveys that aim to constrain galaxy formation using the CIB. In this context, my graduate endeavors will be especially useful for soon-to-come experiments, since they are novel approaches that improve late-time cosmological probes.