"Writing into stone" some tools and links that have help me learn and improve my designing skills. This can actually come in handy for any other product designer out there, so let me know if it helps!
The Noun Project
Find examples of icons you want to create. Google but for icons.
iPhones, Macs, Google Pixels, Samsungs, etc.
Sketch App Resources
Quickly search for social icons, mockups, or others.
Toptal's HTML symbols collection
Find any text arrows, text hands, or any other weird symbol.
Shift Nudge Course
Very expensive but maybe something to keep an eye for.
That Portfolio Book
If you give your email you can take a look at the first 2 online chapters.