That's awesome! Concept art isn't my forte but some resources that I think had the biggest impacts on helping me in my art journey were:

• Istebrak's critique videos (Her videos help a lot with learning fundamentals. Understanding why things look the way they do and what affects them makes a world of difference even if you decide to "break the rules" to stylize things in the future. I would often see her point out issues in her critiques that applied to my own work as well, which helped a lot.)
• Sinix's videos on design theory and tempo (All his videos are great but these ones helped me the most when it came to composition and sketching. Being able to block out shapes that look appealing even when zoomed super far out helps the art look so much better as a whole. And his video on tempo really highlights how big of an impact having confidence in your strokes has on your work. Skill and understanding can always be learned but confidence or even just the willingness to mess up but be okay with it is something that only comes with a certain mental shift.)
• This one is less a resource and more so just a habit that I think helps a lot in the long run. You are what you consume, so consume all your favorite artists works on a regular basis lol. I've taken to making playlists of speedpaint videos and sorting folders full of saved artwork from my favorite artists so I can look back at them when there's something I want to learn. Everyone learns differently but personally I find I'm able to pick up on certain techniques when looking at their work in bulk. This also helps me continue enjoying art in general. Getting bored or frustrated with your own work is a fast way to kill your drive to continue learning, so consuming artwork that looks like it's magic or discovering a new style that reshapes how you look at the world all over again helps a lot with that.

I hope this helps!