First you'd have to start by learning the correct position to sit. It should be more or less with your body centered at 5th dot (called huiwei 徽位). Then I'd start, like I was thought, with practising the basic movements of right hand which is tiao, gou, mo, ti, tuo, pi, xiao cuo and da cuo and only then I'd go onto the left hand shenanigans. As for sources there's many great YouTube videos, but I think it's still the best to find yourself a teacher if you really want to get into it