In Jake’s own words:
SVGOMG is SVGO's Missing GUI, aiming to expose the majority, if not all the configuration options of SVGO.
Hand SVGOMG your SVG either by uploading the file or pasting the code and it’ll strip out all of the editor’s metadata, comments et cetera. From there, toggle the (extensive) options as needed until you’re happy with the preview and file size then download the compressed SVG or switch to the code tab to copy/paste it out.
I typically get anywhere between 30 and 60% savings when running SVGs exported from Photoshop or Illustrator through it—occasionally more.
To get an idea of everything that’s going on to make files smaller, you can check out all of SVGO’s current features.
The only hitch I sometimes run into is elements of the SVG getting hidden once imported and compressed. When that happens, turning off the “Remove unused defs” option always fixes it.