Useful links

Fonts:

https://fonts.google.com/

https://www.dafont.com

https://fontba.se

https://www.fontspace.com

Typography:

https://www.monotype.com/font-pairing#/playground?fontPair1=Milo+Pro&fontPair2=Pona+Book

https://www.whatfontis.com

https://www.lipsum.com

Color theory:

https://coolors.co

https://www.canva.com/colors/color-wheel

Mockups:

https://www.freepik.com/search?format=search&last_filter=query&last_value=&query=&type=mockup

https://mockupsforfree.com

https://www.graphicpear.com

https://unblast.com/mockups

https://mockupfree.co

https://www.pixeden.com/free-graphics

Icons:

https://ionic.io/ionicons

https://iconoir.com

https://www.graphicpear.com

https://www.svgrepo.com

Stock images:

https://www.pexels.com/search/free

https://www.freepik.com

Inspiration:

https://dribbble.com