Do you know common web configuration stuff you will need?

In SharePoint, web configuration includes:

1. ASP.NET 3.5/4.0 library references – this is necessary for all the ASP.NET AJAX calls
2. Add system.web/pages/controls – to add additional tag prefix from System.W eb.Extensions
3. Add HttpModule (for example – to clean up extra JavaScript from SharePoint)
4. SafeControl tags for all custom dlls – in general these can be added via your solution package as well

You should always use a SPConfigModification class to modify your web.config – never tell your user or administrator to make changes manually!  This also allows them to switch off a feature from SharePoint knowing that the changes had been reverted. For developers – you must test your SPConfigModification carefully, mismatched XPath will cause problems in your web.config and create duplicate entries!