DC timing violation, what to do first?

Hi all,

I am new to Synopsys DC. And I have a basic problem. When I find timing
violation in DC re****t, what shall I do first?

1. Shall I change the script of DC? To let the tools do something like
retiming?
2. Shall I change the RTL code? To pipeline the comb logic manually?
3. Other choice, please recommend.

What circumstance to do "1" or "2" or "1 and 2 at the same time"?

Best regards,
Shenli