hey!
there is lot of videos and info available about building multicopter,but there is not much usefull info about tunning it for stable flight,well for that i am gonna share up my little exp about this topic

points to remember,

1.quality parts:a quality parts is the most imp thing in a multicopter to fly perfectly and avoid crashes,well newbie always look out for better cheap options,but a best suggestion for them is get quality parts or else you gonna loose everything,

2.mounting the fc:mounting the fc to the center of thrust.there are some pages which tells its not imp to mount the naza on the centre of gravity, but i have gone through certain experiment in which its been proved that mounting the fc to the ct is a must thing for better stable flight
[i had dji f450 with naza lite mounted on the bottom plate of the craft but i when i changed the position from bottom to upper plate it behaved much better than before

3.vibration dampers:excess vibration from propulsion system is the another imp factor for unstable flight this issue is solved by using the vibration dampers for flight controller+using better quality prop motor esc,as quality parts come up with proper balancing+and always balance your props for better flight experinces

4.give some time to balance your cg of multicopter

5.mounting the gps properly,if this part of copter is ignored it can be the reason for some improper flight

6.gains are the most confusing and irritating job on a multicopter,well it need proper understanding and need proper time for experiment for setting up the gains,depending upon the flight controller,

7.calibrate your esc

8.esc firm,it should be simonk or bl heli,there are some newbie who spended money in buying airplane esc, well this thing not gonna work on multicopter better remember this point

9.always do gps calibration.if you are a naza user or you using any gps enabled fc imp point is to calibrate your gps before each flight session this will avoid flyaway,and better home lock

10.always install gps on a gps mount so that it will stay away from magnetic interference produced by esc or wire which carry current