A cube is a machine. Treat it like one.
Most of what people call a "bad cube" is really just a tight, dusty, un-adjusted one. A few minutes of actual maintenance does more for how a cube feels than any amount of practice.
Buy a modern cube
The original turns like a rusty hinge. A cheap current speed cube corner-cuts, self-aligns and costs less than a paperback — it will take ten seconds off your time before you learn anything.
Loosen it properly
Most cubes ship far too tight. Turn the cube so a corner points at you, and you'll see a small screw at the centre of each face — usually a flat-head under the centre cap, sometimes a tensioning nut. A quarter to half turn looser on each is the usual sweet spot. Too loose and pieces pop out mid-turn; too tight and it catches. Adjust a little, test, adjust again.
Lube it, sparingly
A drop or two of silicone-based cube lubricant per face, worked in with a few dozen turns, transforms the feel — corners glide instead of catching. More is not better: too much lube makes a cube feel mushy and attracts dust. Once every few months of regular use is plenty.
Fixing a popped piece
An edge or corner jumping out mid-turn is not a breakage — it's a loose or misaligned cube doing what loose cubes do. Line the piece back up with its neighbours at roughly the angle it came from and press it firmly back into place. If it keeps happening on the same turn, that face is too loose or slightly misaligned; tighten it a fraction.
Never force it
If a face will not turn, another layer is misaligned by a fraction. Straighten it rather than pushing — that is how corners get chewed and cubes get popped.
Mind the heat
Cube plastic warps in strong, sustained heat — a hot car dashboard or direct summer sun through a window is enough over time. A cube that no longer sits quite flat usually got left somewhere too warm, not damaged in use.
Turn with fingers
Beginners rotate the whole cube with both hands. Fast solvers flick single faces with index fingers and thumbs while the cube stays still. Practise the flick before practising speed.
Learn to look ahead
The clock runs while you search. Solving slowly but continuously beats solving fast in bursts, every time.
Colour scheme is standard
Almost every modern cube has white opposite yellow with green, red, blue and orange around the middle. Learn that layout once and any cube is familiar.