When you are developing a custom solution for CRM, you will undoubtedly be required to restart part or all of the system to get your changes to take effect.  Here are some guidelines that I use to determine the minimum amount of work I must perform to implement my changes.

Entity Customizations

Publish the entity in question or Publish All Entities just to be safe.  Usually, a CRM system restart is not required.  This includes changes to the CRM schema, and any Form or Attribute Events you may have implemented.

Callouts

Require an IISRESET. Should you need to implement a update to a callout already within the system, performing an IISRESET will unload the callout, allowing you to replace the old DLL with the new version.

Workflow Assemblies

Stopping and Starting the CRM Workflow Service will release any loaded workflow assemblies and allow you to make changes to the workflow config file.

Sitemap

The sitemap is implemented immediately after it has been imported.  When you doubt, perform an IISRESET.

ISV.CONFIG Changes

When implementing solutions that involving changing the isv.config file, I always like to perform an IISRESET afterwards, just to be on the safe side.  However, I have noticed lately that changes made to Entity toolbars, for example, will be picked up and displayed the next time the Entity record is opened.  Still, an IISRESET is always a safe bet.

Custom Web Pages ( linked to CRM via ISV.CONFIG )

If you are making changes to a web page that you have linked to CRM via the isv.config file, you may not always see your changes implemented. This is due to the fact that Internet Explorer caches the pages locally and it will retrieve the cached copy first. To circumvent this issue, simply empty the cache ( Tools, Options, Delete Temporary Files ).

Well, I think that is all I have noticed recently, but if anyone has additional best practices, please let me know.