Standard suspension settings crf250R

I'm assuming you mean 170 pounds rider and not 170kg lol. 

First thing is to write down all the clicker settings before you change anything so you can always go back to stock. Second, set the sag to 105mm it is the most important setting for bike balance. 

Here are two sets of recommendations on settings (the mxa are more stiff / hardcore racing)

https://www.keeferinctesting.com/2024-honda-crf250r-baseline-suspension-settings-tips/

https://motocrossactionmag.com/mxa-race-test-the-real-test-of-the-2024-honda-crf250/

In sand, generally you want to go stiffer on all clickers to make the suspension slower. Drop the forks to flush with the clamps to increase stability.