An excellent reference to RTL coding guidelines is the popular Reuse Methodology Manual
**broken link removed**
Almost all Lint tools come with rulesets that will check your RTL for this compliance.
Also, books on HDL synthesis will help you understand the rationale, such as HDL Synthesis Primer by Bhasker.
As an extension of this, in Verification there is VMM - Verification Methodology Manual, though it is much much more than just coding guidelines. See www.noveldv.com or www.vmm-sv.org for more.