My biggest mistakes have been:
1. Guessing heights that are too low. Trees can be very tall you don't truly get to a safe alt till 200+ feet in taller tree situations.
2. Using the banking and adaptive turn modes can greatly affect the path of the phantom as it looks to efficiently turn between waypoints. It's not a bad thing but you need to be prepared that in a square with banked turns (for instance) the right angles will be cut off significantly. Not a problem if you're at altitude but if your at a lower altitude... Tree you were thinking your were going around could suddenly be in your path! Experience talking here lol
3. The altitude under 50 feet or so is pretty unreliable. I have started a flight where the phantom reads 10 ft before take off... And when it lands In the same spot.. It then shows 30 ft on the ground. So I would suggest not setting your altitude at nothing less than 50 or 60 ft for automated flight.
4. You will occasionally lose connection to your phantom via the GS. Happens all the time. Don't panic... If you need to pick up the regular contoller and switch to atti that's fine... But what I do is make sure my starting and ending waypoints are pretty close to me. After it flys it's route... I can rescan for the aircraft as it gets closer again and either hit go home or take control with regular controller to land.
I generally wait till it hits the waypoint right above me.. Hit "go home" and when it's about 30 ft up... Take control with the regular controller and land. It can land on its own.. But can be a 10 meter radius difference from the take off point...
I realize this is a lot... And probably makes your nervous. However I'm just trying to give you the things to think about before you make some of the same stupid mistakes I have (as I write this, I am awaiting delivery of a replacement zenmuse gimbal due to a stupid waypoint/altitude combination mistake I made which sent my phantom into a pine tree just below its peak)
Automated flight is super cool and I have had lots of good flights... It's just a bit odd for people who normally used to controlling an RC quad rather than letting a computer do it

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Good luck!