Use the "DPM++ SDE Karras" or "DPM++ 2M Karras" sampler with only 20 steps for better quality. "DPM++ SDE Karras" has better quality but is slow.
Use the CFG scale between 5 and 9. CFG scale at 5 is recommended. Stable Diffusion default value is 7.
Resolution between 512 and 768 using "Hires. Fix" or other form of upscaling. The 600x600 resolution is the one that has worked best.
If you use "Hires. Fix", use "Upscale by" with the value 1.5 with denoising at 0.6.
Use the "Euler a" or "LCM" sampler with only 8 steps for better quality.
Use the CFG scale between 1 and 2. CFG scale at 2 is recommended.
LCM with DPM++ SDE Karras: Sampling steps 8, Hires. Fix enabled, upscaler latent, Hires steps 2, hires. denoise 0.45, upscale by 1.05, cfg scale 1.5.
LCM with DPM++ 2M Karras: Sampling steps 8, Hires. Fix enabled, upscaler latent, Hires steps 2, hires. denoise 0.55, upscale by 1.05, cfg scale 1.5.
Use the "Euler a" or "DPM++ SDE Karras" sampler with 20-30 steps for better quality.
Enable fp8 in the latest versions of Web UI to save a lot of ram. It can speed up SDXL a lot depending on how much ram and vram you have.
If you are having a lot of trouble running SDXL in the Web UI. Try using Fooocus.