How do I improve my welding on hard positions and tough metals?

You can weld well now, and that is no small thing. Flat, easy runs come to you. What defeats you are the awkward positions and the strange metals, the parts of the trade where the old habits stop working. That is not a wall. It is just the next section of the road, steeper than the last. Do not try to conquer all of it at once. Pick one hard position or one difficult metal and make it your project. Practice it deliberately, on scrap, where a failed bead costs nothing but time. Mastery is built narrow and deep, one difficult thing worn down until it becomes ordinary, then the next. That is how the easy welds became easy too. Watch people who have already crossed this ground. Ask how they set up, how they read the puddle in that position, what they do differently with the exotic stuff. Then go put it under the torch yourself, because the hands learn what the eyes only glimpse. You are not stuck. You are simply mid-climb, and the top is closer than it feels.