Use two hands. Hold the knife by the handle, press down on the lock release cut into the spine, and let the blade swing closed with your other hand controlling the spine, never the edge. Keep the fingers of your holding hand out of the blade's path before you release anything.
Moving your fingers first. On a back lock the release sits partway along the spine, and your natural grip puts the base of your fingers right where the blade closes. Reposition before you press, not after.
See frame lock versus back lock for how the mechanism works.
Hold the handle in one hand with fingers clear. Press the release with a thumb. Take the blade spine between finger and thumb of the other hand and guide it in. Never let it drop freely on a strong spring.
Guide it by the spine, never anywhere near the edge.
A stiff release usually means a new knife rather than a fault, and it eases with use. Do not compensate by pressing harder and snatching, which is exactly how fingers end up in the path.
See the safest way to close a folding knife for the general case.