20ms is excellent
50ms is OK
100ms (or more) may cause rubber banding or other issues.
Rules of thumb for best network performance.
1) Don't use WiFi, the lag is 50x worse. Use an Ethernet cable.
2) When you have CMDR's in your instance, your network connections will be used a lot more. The more CMDR's the more network traffic.
3) Your upload speed is the limiting factor. Try not to saturate it with other processes, Netflix, BitTorrent, YouTube, Windows Updates, etc.
4) Some routers can prioritize some traffic. See if yours can give Elite priority.
5) If router can't do that, your PC network traffic can be prioritized with this program:
https://seriousbit.com/netbalancer/
At the very least, you can see what your static traffic levels are.
Port Forwarding. Doc from Frontier Support here:
https://support.frontier.co.uk/kb/faq.php?id=344