Here are some cool tips / tricks you can do on your Amazon Device.
1. Display Mirroring.
Without using any 3rd party software, its now possible to mirror the screen of you phone on to your Fire TV. To do this, firstly ensure you are running the latest version of FireOS. You can confirm this by going to Settings —- My Firet TV —- About — Software update.
To start the display mirroring, press and hold the home key on your remote

On your smart phone look for an option called “Smart link” or “Display Beam” or something like that. Select the Fire TV and you will now be able to see the screen of your phone on your TV.
2. Close All Background Apps
Install an application from the APP store called “Developer Tools Menu”
Once installed, click on

This will now show you all the apps that are running in the background. On the top left, select the option to “Close all apps”

This will then take you to the apps that are option and you can select the option to “Force Stop”. This will terminate the app and free up memory.
The more free RAM you have the better chance you will have to avoid buffering.
3. Use Bluetooth Devices
You can connect all sorts of Bluetooth devices to your Amazon device. Everything from Bluetooth keyboards / Mice / Headphones and even Soundbars. You can add a new device by going to Settings — Remotes and Bluetooth Devices and add a new device.
4. Use ADB to improve UI performance
We can use ADB to improve the performance of your Amazon device. Firstly we need to install Remote ADB from here
Ensure you have enabled ADB enabled in Settings — My Fire TV — Developer Options.
Open Remote ADB and enter the localhost IP 127.0.0.1 on port 5555

Once connected enter in the this command:settings put system transition_animation_scale 0.0
click Run
Ensure there are no errors and then enter in the 2nd commandsettings put system window_animation_scale 0.0
click Run
The 2 commands will turn off the Window and Transition animations which will give you quicker UI performance
5. Use your Phone to control your Firestick
From the Playstore/App store, download the official Fire TV app. When you launch this app, it will automatically scan your home wifi network and list all of the compatible Amazon devices.
Click on your device that you want to control. You will then see a PIN code on the screen

Once entered, you can now use your phone to navigate around your device. You can also use the voice command from your phone as well as use a virtual Keyboard.
6. Use an OTG cable
You can use an OTG cable on your Firestick which will give you a full size USB port.

You can plug in any USB device including a USB flash drive. You can then access the content on the USB drive and play movies / music in Kodi.
You can also convert the USB drive as adoptable storage and install apps to it. You can see the full steps here