Hi,
Thanks for your advice. Please shed me some light on following questions.
1) How long should I invest to learn flying the drone, approximately.
2) Will a small foot ball ground provide me sufficient space for learning its flying.
3) What other points I need paying attention to on learning
When you know why & how a DJI drone can fly stable... even during outside influence (like windy weather), and how it can hold position when just hovering... and more important, when & during which circumstances it no longer can't, then you might have sufficient knowledge to do proper risk assessments regarding putting a camera up in the air.
When it later comes to the different automated flight modes (like Follow Me or Tracking) they on their own have limitations & requirements that you need to understand in order to utilize them properly & without mishaps & crashes.
Flying drones require an array of different understandings, knowledge & experiences in order to be safe & being under YOUR control... & not just being sheer luck that the drone returned to you in one piece (a not harming yourself, somebody else or something in the process) with a video result that you can use.
So... how long will it take to learn all this and being a safe & confident drone pilot... in general impossible to answer I'm afraid. I'm recommending you to treat this with drone flying as a side hobby until you've reached a level of confidence where you feels that you can safely merge your videoing interest with drone flying.
Besides all above (which is crucial in order to foresee risks) you also have the plain process of flying, launching, landing, disconnects, apps, obstacle avoidance, sensors, heights, battery management & care, propellers, pre flight checks, magnetic disturbance, calibrations, flight logs & flight regulations.
Below are the bare basics of flying a GPS supported camera drone...
Read the user manual...the thick downloadable one, not only the quick start coming in the box, download here -->(DJI's product page for the drone model in question)
Power on in the right order... First power on your RC & start the app... after that, power on the drone (& do it on the spot you're going to take off from). Reverse order to shut down.
Preferably power on the drone keeping it horizontal in your out stretched hand (without watches, rings or other magnetic objects) … once the live view have turned up in your mobile device you can put it on ground for take-off. (This supports the point below…)
Before take-off ALWAYS... add in one very easy check to avoid a really scary event coming from accidentally launching from a magnetic disturbed place with following flyaway at height in an uncontrollable circular or straight flight path. After powering on your drone, connected to your RC/app & placed it in the take-off spot... but before lift-off,
ALWAYS check that the drone icon on the map in your app is pointing equal in relation to other objects in the map as the drone does in reality... if not, abort launch attempt,
POWER DOWN & move away, power up again and repeat.
Keep well under the wind spec where you fly ... and please note that it's not only at ground, it's at
the altitude where you fly. The winds up to 400ft are very different then on ground. Use for instance the UAV Forecast app where you can get a feeling about the winds on higher altitudes, but please note that it's forecasts we are speaking of, a bit of common sense is good to apply to that...
"better skip flying a windy day & fly more another".
Don't go & calibrate everything on a regularly basis... why fix things that are working, it's just a higher risk that you by mistake calibrate your compass in a magnetic disturbed area & the drone goes haywire 10 meters up in the air. Calibrate IMU + compass according to user manual, keep away from magnetic things like cars, metal tables & reinforced concrete at take-off & compass calibrations. If the app recommend a compass calibration first try another launch spot on a far distance from the first... if calibration still is recommended by the app do it, but only then.
Don't launch in a hurry... wait until you have sufficient number of locked satellites & wait for the lady voice in the app to announce that the Home point has been updated, check then on the map that it's in the correct spot. Learn how the RTH function works (it can work differently depending on scenario & drone model), don't set the altitude for that unnecessary high, look around were you are going to fly and set it to clear the highest obstacle, to high & the drone risks a blow away.
Seek up a large open place... a soccer field, free of obstacles & people. Test off every function one at a time until you fully understand how it works & the logic behind, confirm through the user manual if needed. Fly low, slow & near.
And don’t try to fly indoors before you exactly know what makes these machines fly stable … you only risk your interior & to damage your drone in the process.
Take the claimed control distance from DJI with a pinch of salt... only doable out in the countryside completely free of WiFi disturbance & obstacles in between the Remote & Aircraft.
Don't rely 100% on the obstacle avoidance sensors... they are good & handy to have to perhaps save you when making a mistake, but they can't see everything, especially thin branches & wires so don't think they will allow your drone to just bounce away from everything all the time. Also note that they need plenty of light& a GPS lock to work properly, too dark or no GPS position & they will turn off.
The Pause button on the RC... It's a handy one, it will stop all automated modes immediately (if you have GPS coverage). Place your thumb on that when you initiate an automated flight mode & be prepare to stop it if too close to a tree for instance.
Don't use the RTH button as a "panic button" it's usually the weakest mode of them all... you will always have access to more power in the manual modes... if slow against a bit to strong head wind, go for Sport mode, drop altitude & manoeuvre the drone home manually.
Learn the rules & regulation ... keep the drone within Visual line of sight & respect max altitudes, if you can't avoid going out of visual keep it at least in line of sight (unobstructed line between Remote & Aircraft even though you don't see it) so you don’t lose the connection.