For EPiServer: Remove language files not used.
Have SQL Server as "near" as possible. There's a lot of traffic between the EPi-app and the db before the first request is served completely.
For ASP.NET websites in general, this setting in web.config will do wonders:
<compilation ... batch="false"> ...</compilation>
Beware of some side effects though depending on what you're doing.
More info about slashing ASP.NET compile load time:
Any tip/ideas/parameters to decrease the ASP.NET start time after re-compile?