Building from Source
One good practice is to build software from source in the home directory
for just the user, e.g. in ~/bin. This normally involves cloning the
software repo to this directory and running the build command there.
From there, one can run the executable to open the package.
See Current setup under Linux for more information on currently used standards for where to keep packages installed from source etc.
mu
A very peculiar case was build mu from source. Since there was no
./configure file, one has to DESTDIR=/path/to/staging meson install -C builddir
(from documentation here) to install to it to the user directory, after generating builddir in the project root directory.
emacs
Use the flags in the StackOverflow question here. Note this may mean having to install dependencies like for treesitter mentiond here.