It is important to minimize compression of your reserve. Air between the folds of fabric help it to open quickly. Compression is almost impossible to avoid, and is the main reason we repack our reserves. However, you can help by not sitting on it and taking care when packing your harness in the backpack. Moisture in your reserve container should be avoided. If you suspect that your reserve has become damp, open it up to dry, and have it repacked as soon as possible. When they get wet the air is forced out and it will compress as it dries. Note: do not dry it in the sun, reserves do not have any UV protection and UV is very detrimental to the fabric.
Keep dirt and debris out of the harness container, as they are abrasive and can damage the lines and fabric. It’s a good idea open the container and clean it out periodically, especially after being around sand. Over time and with exposure to heat and moisture, the rubber bands holding the lines will break down, allowing the lines to become entangled. For recreational pilots, it is recommended that you have your reserve repacked every 6 months to a year.
As part of your preflight you should already be checking your reserve handle and pins. If your handle is attached with velcro you should be conscious of velcro-lock. Over time two pieces of velcro may become locked together such that they are extremely difficult to pull apart. You should pull your reserve handle velcro apart once a month to ensure it releases easily if needed.