For the most people probably Captain Obvious is calling, BUT I get used to a little visual studio option:
“Track Active Item in Solution Explorer”
Check this option and the file you are currently editing will always be highlighted in the solution explorer of VisualStudio, even if it’s in another project. The corresponding tree will be expanded automatically. In the past I got this behavior only with VisualStudio Extensions, but now I know, that this isn’t necessary any more.