Q) Typically it is good practice to add series resistances to clock and signal lines. But what is the best value?
A) We do not recommend any particular values/range for resistors.
Please refer our application note from the link given below : ( Cypress Serial Peripheral Interface (SPI) FL Flash Layout Guide)
Please note that the device S25FL164K0XMFI011 is not recommended for new designs and is obsolete. Please refer the product termination notice PTN from the link given below :
The recommended replacement and the Migration application note is mentioned in the folder present in the above link.
Good answer for my question is here:
There is info that it is good practice to add series resistance on the high speed lines.
Value of these resistors depends on the traces impedance and reflections.