Clean your equipment. You should keep machines dust-free. Dirt and grime that accumulate inside your machines will affect their performance. Wipe down your equipment on a weekly basis with a clean towel and detergent. Be thorough, as it is the places least visible where dust can accumulate quickly.
Lubricate the guide rods on any weight machines with lithium grease or silicon spray. Guide rods are the metal rods that go through the center of the weight plates. Without lubrication, you will notice your weight machines starting to feel more resistant to motion. It is not because lifting weights is making you less strong. It is because the guide rods, when less lubricated, start becoming stuck in their rest position. This happens very gradually and so you will only need to lubricate the rods one to two times a year.
Check the cables on your home gym equipment every few weeks to a month. When a cable is visibly worn (pinched or fraying) or stretched, you should adjust or replace it before using the equipment again. The documentation that came with your machine should have information on either adjusting or replacing cables. This will vary depending on the type of machine and manufacturer.
Inspect the bolts on your machines. Loose bolts can be dangerous as they increase the likelihood of a piece of the machine falling off during use. Once a month, test the various bolts on each machine in your home gym by holding it with your thumb and forefinger and applying slight pressure counterclockwise. If you find a bolt that moves with only slight pressure, tighten it with the appropriate tool.
Use your home gym equipment as it is intended to be used. Each piece of gym equipment is designed for very specific exercises. Experimenting with alternative exercises for a weight machine that you do not find anywhere in the documentation that came with it can be dangerous and also potentially break your machine.