Move your fingers clear of the blade's path first, then release the lock, then guide the blade in by its spine with your other hand. Never let a blade drop shut under spring pressure, and never close a knife one-handed simply because the design allows it.
Almost every folding-knife injury during closing follows the same sequence: the lock is released while a finger is still in the arc. Deciding where your fingers are before you touch the lock removes the whole class of accident.
This applies to every lock type, though the finger position differs between them.
On a liner or frame lock, push the lock bar aside with a thumb and guide the spine with the other hand. On a lockback, press the spine release with fingers repositioned. On a slip joint there is no lock at all: the backspring resists, and a half-stop breaks the movement into two safer stages.
Slip joints deserve extra care because nothing prevents the blade closing on a finger under pressure.
There is no benefit to closing a knife quickly. Guide it in deliberately by the spine every time and the habit becomes automatic.
If a knife is too stiff to close comfortably, see breaking in a stiff new folder.