Clean all your instrument jacks and DC power jacks with electronic contact cleaner! I recommend DeOxit D5. Spray a small amount in all of the jacks and work it in with the corresponding cable. This keeps your jacks from rusting and keeps them in tip-top shape.
Check all of the connections for your instrument cables and DC plugs. Avoid tight corners/turns with your cables. This adds unnecessary stress to the cable and makes it prone to failure. Using the right length cable is important. Additionally, cables can go bad over time. Replace cables as needed.