the best advice i can give when drawing from your mind is always have a good outline before you start like if you're drawing people know your anatomy and draw a stick figure with all the correct poportions use a lite pencil to do this like a hb or a 6h so it can be easy erased then you can build up from that. Every picture i draw i do this even if i'm ussing reference. it's kinda like a sculpture making a wire aramature before they use clay. a lot of people ask me about this keep your eyes open i may do a lil step by step to show people how i draw. but keep in mind what works for me may not work for you tryout lots of styles to you find one that fits, i hope this was helpful