This is from another forum (AT&T)
Or this site
If you have the FIOS G1100 router, make sure the Fire Stick is connecting to 5Ghz Wi-Fi. If you have an older ActionTec router, check the Wi-Fi performance using a speed test app near where your Fire Stick is situated. The iPhones have a smaller antenna array and should test accurately enough to the Fire Stick's capabilities.
If your Wi-Fi is getting saturated because you're streaming at 1080p+ while other devices are using the Wi-Fi, and you're using an ActionTec, it's probably a good idea to consider getting a router with 5Ghz support to see if it helps.
Now the free option is, you could try changing the DNS Servers your router is using to Google DNS or OpenDNS. 188.8.131.52 and 184.108.40.206 are Google DNS, and 220.127.116.11 and 18.104.22.168 are OpenDNS. This doesn't chnage your routing, but can affect what servers on Amazon's CDN (And other services) you end up hitting.