I would suggest first to try altering pre-existing assets. Take assets RPG Maker already provides, then: change a character's clothing and poses; add a cup of coffee in their hand; alter a table leg so it's fancier; make a hen into a rooster; create a galloping version of the horse sprite.
All the while, pay attention to how light and shadow is portrayed (notably, most JRPG/RPG Maker assets have light coming from the top left of the screen, so the shading is on the bottom right). Don't go easy on yourself if your characters' limbs come out disproportionate or lopsided, or when a pose looks unnatural. Don't say it's good enough and move on; fix the wonky parts early, and learn early.
Your custom assets, if being used alongside assets from other sources, need to match. If you can't make all your game's assets match (lighting, color palette, style), then your learning isn't complete.
From my experience, what's helpful to remember is that you're creating assets pixel by pixel. Getting impatient and trying to draw in broad strokes usually gives you wonky results (which, at best, can be fixed when you zoom in and edit the image pixel by pixel).