It's called the Hop-Up Launch (or at least, that is what I call it).
Common sense (and many how-to guides) will tell you to slowly increase your throttle in order to gradually lift your drone off the ground. The problem is, many drones will immediately start to tilt to one side, or even topple over if you go slow.
I have found this to be true of little drones (like my new CX-30s) and of big drones too (like my Cx-20). Once they get up, they can hover nice and steady, so it is not necessarily a matter of adjusting the trim.
The problem is mostly due to “rotor wash” – which is air turbulence caused by the spinning rotors. Since the drone is sitting on the ground, the rotor wash doesn't have anywhere to go, it all stays immediately around the drone – which can cause the drone to have trouble taking off smoothly.
The trick is to “jump” the drone into the air a few feet, and then level it out and work on any trim adjustments it may need.
To perform a Hop Up Launch, quickly bring your throttle up so your drone jumps a few feet into the air, then bring the throttle back down to settle it into a hover.
It takes a little practice – be careful not to overdue the throttle and launch the drone way over your head! After a few attempts, you'll get the hang of it.
This is now my default method of launching drones big or small. Give it a try!