[nanna]

More on creating your own class file:

https://www.overleaf.com/learn/latex/Writing_your_own_packag...

How I do it...

I keep a directory called LaTeX inside my home directory. Inside that I keep a file with all my frontmatter, myfrontmatter.sty (technically a package rather than a class), and also my biblatex file and a scan of my signature for signing letters. When I start a new LaTeX document I add the line \usepackage{/home/nanna/LaTeX/myfrontmatter} to the top (note, no .sty). This keeps my frontmatter minimal and tidy.

Inside myfrontmatter.sty:

  \NeedsTeXFormat{LaTeX2e} 
  \ProvidesPackage{/home/nanna/LaTeX/myfrontmatter}[2015/01/01 by me]

  \RequirePackage{amsmath} % Just replace `usepackage` with `RequirePackage`
  \RequirePackage{amsthm}
  ...

  \addbibresource{/home/nanna/LaTeX/biblatex.bib}
  ...

  %% Macros like for inserting my signature
  \newcommand{\mysignature}{\noindent\includegraphics{/home/nanna/LaTeX/signature.png}}
  ...
  \endinput % Not sure if this line does anything?

And that's it. I never have to worry about a package I've forgotten to add in. Granted a journal might not accept my custom package but I can always just copy and paste it all into my frontmatter, minus the top two lines and replace all the RequirePackages with usepackages.