The most useful thing you can do for sliding windows is to keep the tracks in which they slide clean. Depending on their width, try using a toothbrush or a larger stiff brush to loosen the dirt and use a handheld vacuum to remove it. Wrapping a cleaning rag over a flat-bladed screwdriver also works well. To help the windows slide more easily, rub a wax candle in the tracks.
Large sliding windows sometimes have rollers on the top and/or bottom of the sashes. They can gum up with dirt or grease over time, so a shot of silicon spray can help keep them clean. If they're broken, take the window out of the frame, and have it repaired by a professional.
To replace the glass in a wooden sliding window, or to repair loose or broken corner joints, follow the directions for wooden sash windows. For metal windows that have loose corner joints, look for a corner screw that can be tightened gently (overtightening it could bring the window out of square enough to break the glass). Some weather stripping can also be replaced by removing a corner screw that holds a metal channel in place. For other repairs, seek out a glass professional who has the tools and expertise to deal with the ways these windows are put together.
Whenever you're cleaning the tracks, check that the small holes through the window frame aren't clogged (use a paper clip to poke out any dirt). These weep holes are designed to let water such as condensation escape, so they need to be kept free of debris.
The catches that hold sliding windows closed can wear out, no longer locking the window securely, and in some cases, not engaging the window at all. If it's a metal catch that's bent, try using pliers to bend it back into place. Bent plastic catches need to be replaced. Consider buying metal catches, which last longer and are more secure. Just make sure that the replacement catch will fit over and hold the window properly.
The screws that hold catches in place can loosen. Use the quick fix for door hinge screws in Chapter 3 to solve this problem.