I have a bunch of common commands I put in document preambles. I don't always use them all, but it makes the preamble too long for my tastes.

I want to put them all in an external file (preferably in my user texmf tree). A class file seems like overkill; it isn't robust and I don't know TeX anyway. Creating a package seems intimidating as well. Can I just put the macros in a `macro.tex` in my tree and use `\include{macro.tex}` in my preamble? Also, could I include the same after `\begin{document}`?