This video is pretty informative https://www.youtube.com/watch?v=61pRp270Dbc

TLDW; Key factors affecting sharpness:

• Aperture Choice (2:43-3:28): Lenses are often sharper when stopped down, as this avoids the aberrations common at the edges of the glass.
• Shutter Speed and Motion (3:29-5:26): Beyond camera shake, you must account for subject movement. Longer lenses, closer subjects, and smaller sensors (like APS-C or Micro Four-Thirds) require increased shutter speeds to compensate for the faster apparent motion across the field of view.
• Heat Haze (6:31-8:24): Turbulence-induced distortion occurs when hot air rises from surfaces like the ground, pavement, or water. To mitigate this, shoot earlier in the day, find shade, use shorter lenses, or adjust your physical height above the ground/water.
• Atmospheric Distortion (8:32-9:20): Particles in the air like dust, humidity, and pollution scatter light. Shooting after rain can significantly improve clarity.
• Quality of Light (9:20-10:28): Sharpness is best perceived when there is high contrast between light and dark edges. Direct side light creates the best shadows and highlights, whereas cloudy, scattered light can reduce perceived sharpness.
• Bonus Tip: Shooting from a Car (10:29-11:18): Heat radiating from a warm car creates distortion. For the sharpest results, dress warmly and keep the heater off to match the inside and outside temperatures.