I have the following convention for most of my projects:
/src
/Solution.sln
/SolutionFolder
/Project1
/Project2
/etc..
/lib
One more little tidbit that I just discovered. (This may be so basic that some haven't mentioned it, but it was important for my solution.) The "packages" folder ends up in the same folder as your .sln file.
We moved our .sln file and then fixed all of the paths inside to find the various projects and voila! Our packages folder ended up where we wanted it.