At Exclaimer, we see a lot of email signatures. We see what a lot of companies get right and what they get wrong.
DO use the right tools
Remember that this is a signature and not a word document, a web page or an image on its own. If you know HTML, you need to code it accordingly.
If you don’t know HTML, don’t use Microsoft Word or Outlook to draw your template. Any other program (or another version of that same program) may interpret the layout differently and display it incorrectly.