The Dark Energy Survey (DES), an international collaboration whose main goal is to unveil the nature of dark energy. For this purpose, it has performed a 6-year photometric survey from the Blanco Telescope at Cerro Tololo (Chile), covering nearly 5000 deg2 of the southern sky with the filters g, r, i, z and Y and reaching magnitudes up to i = 23.7 and redshifts of about 1.2. One of DES's most powerful probes to constrain cosmological parameters is the angular galaxy clustering, described by the two point angular correlation function, w(θ), especially when combined with weak lensing measurements, the so called 3x2pt probe. As part of the measurement, we must take special care of any spurious signal introduced by spatially varying observing conditions and survey properties, such as exposure time and seeing, or astrophysical sources of contamination, like galactic extinction or stellar density. In this talk, we will introduce the systematic decontamination procedures applied for the analysis of the first three years of data (Y3). We will also cover the validation of these methods and the challenges that were faced during the process (and will be in coming cosmological analyses). Finally, we will showcase the measurement of w(θ) in two different galaxy clustering samples used in the DES 3x2pt Y3 Key Project.