First, if you don't already have one, get a good dark cloth. With plain ground glass in my 9x12 cm plate camera, even just using a black T-shirt as a dark cloth made a huge difference in what I could see in the ground glass -- focusing was easier, and I can see the image all the way into the corners, which I never could with just the folding hood supplied with the camera's ground glass back.
Second, consider upgrading your ground glass -- first, if it's not new and very clean, find out how to remove the glass, clean both sides carefully (I've used dish soap for hand washing dishes), and dry with a lint-free cloth (rather than air drying, which can cause water borne minerals to deposit in the texture of the ground side of the glass), before reassembling (be sure you get the ground side of the glass in its original orientation). If the glass isn't pretty fine textured, think about replacing it with a new one from Satin Snow, and if it's still not bright enough under the dark cloth (and the corners can be rather dim if you have a wide angle lens -- shorter than about 150 mm in 4x5) think about a Fresnel lens overlay -- you can get these in various price levels, the cheapest being the full-page book magnifiers sold in dime stores for a dollar or two; cut with sharp, heavy scissors to match your ground glass size with the center of the magnifier centered on the glass, and simply drop into place, textured side of the Fresnel against the smooth side of the glass (the plastic Fresnel can be retained with transparent tape, if needed). This will greatly increase the size of the bright center area and reduce the amount of head movement needed to see the corners and edges of the image.
Beyond that, practice...