When you're getting fitted for glasses, your optometrist will often ask you to compare two potential lenses by alternately showing each of them ("which of these lenses is betternumber one or number two?"). Although it may take some time, eventually you'll settle on the set of lenses that are best for your eyes. You can use a variant of this approach to help your customers see which priorities are best for them, as customers often have trouble "seeing" which features are the highest priority, especially if you're asking them to compare several features at the same time.
Start by writing one feature each on large index cards. Shuffle the pile and put them face down. Take the first one from the top of the pile and put it on the wall. Take the next one and ask your customers if it is more or less important than the one on the wall. If it is more important, place it higher. If it is less important, put it lower. Avoid placing the item at the same level; try hard to rank each feature. Repeat this process with all your feature cards, and you'll develop 20/20 vision for what your market really wants.