The main two parameters are scan rate and step size. Slower scan rate means giving more time to acquire the data at every point (i.e better to do at slow scan rate). and smaller the step size means you will have more data points i.e better fitting of curve. So, you need to optimise the time per step.

Scan step and scan speed impact on the accuracy. Their decrease improves it. For high angles its better to use variable divergence slits. Also look at all slits and masks, they should be adjusted for the largest irradiated area on the sample and you should watch for X-ray good focusing on the sample.