1) Some newer phones like Samsung S9, etc. either do not work with Tello or are not fully functional, may record video but not photos, etc. Hopefully Tello will correct this in firmware. Check to make sure your phone is compatible.
More info: Updates have made the Tello work with more phones (as of 8-18-18).
2) If you leave the Tello craft ON without flying, while updating, connecting Wi-Fi, whatever, it may overheat, shut down and you will get error code 205 (overheating). The manuals do not mention this.
Tello gets quite hot on the bottom, even in normal operation. Be aware!
3) Wind or gusts (over 4-5 MPH ???) will adversely affect Tello. Don't take the risk or be mislead by YouTube videos.
4) A GameSir T1d Bluetooth controller (must be T1D, not another model) is specifically made for the Tello, and allows easy and precise control of the Tello. Again, make sure your phone is compatible.
5) To download updates to your phone Tello App, connect it to the internet. Then, to download that update to the Tello, connect the phone to the Tello Wi-Fi.
Also, in normal operation, be aware that you may need to force the phone to reconnect to the Tello Wi-Fi. Using the T1d controller, it may be necessary to force the phone Bluetooth to connect to the T1d.