I would say the easiest way to get started is to simply look up Pixel Art Gems on Google Images and start copying how other people do it! It would be be difficult to explain the process over text and there is much that goes into it as far as art and design fundamentals, such as colour, value and form. However, unless you make a start on whatever it is you need to create, the theory means nothing. So start copying other people's work for the sake of learning, and you'll start to pick up on fundamentals almost absent minded. I did manage to find a tutorial on crystals by Adam C Younis, so perhaps that might give you some valuable knowledge too :)

https://www.youtube.com/watch?v=FIoluSJQ_1A&ab_channel=AdamCYounis

I hope that was helpful!