1. Go hard wired.
Connect your PC or gaming console to your router with a network cable. This allows your connectivity to be more consistent and reduces the blips that cause jitters.
2. Reduce connected devices.
By reducing the number of devices connected to your network, you are also reducing packet conflicts. If you are using WiFi, reducing number of devices operating on the same channel.
3. Stop your downloads.
In general avoid large data file transfers going over the same WiFi environment concurrently with your gaming console/pc.
4. Avoid buffer bloat.
Buffer bloat occurs when your router is unable to send all the packets needed, and builds up a large queue. This queuing causes large latency and bursts of jitter. With the real-time nature of gaming means this is not helpful.
5. Lower your buffer size
Configure your router with a low buffer size. Many routers have this option built in. I suggest googling your router brand for quick steps.