Your set-up in the hack decides whether the stone starts on line: foot position, 50/50 weight, stone and broom aligned, plus a quick check before every throw.
The honest answer: you can't win a throw in the hack, but you can already lose it. Curling Canada's federation teaching material builds the delivery in four phases: set-up, drive, slide, release [1]. The set-up is the first, and its goal is unspectacular: stand almost exactly the same every time. According to the national coaches, the whole purpose of the delivery is to hit line, weight and rotation consistently; the key word is "consistently" [1].
How hard is it? The position is physically easy, but many small details must come together: feet, knees, hips, shoulders, stone, broom, grip. There is no timeline. Practise it first without a stone, then with one.
This guide covers only the starting position. The drive and the slide are in the follow-up guides.
Press the ball of the anchor foot (gripper) firmly against the hack, laces pointing at the target [1]. According to the rules, the hack itself is at most 152 mm wide (about a hand's breadth) and its inside edge sits 76 mm from the centre line [2].
Milestone: Your foot stands without you having to readjust.
The heel of the sliding foot is level with the toes of the anchor foot, both feet parallel, with 2–3 inches (5–8 cm, about two to three finger widths) between them [1]. Distribute your body weight 50/50 across both feet [1].
As you lower yourself, the knees stack over the feet and the hips are square (perpendicular) to the target line [1]. The shoulders are also square to the target line and level with the ice [1]. A simple check: your shoulder line is parallel to the ice surface, not slanted like a slide.
The stone sits between the middle of the hack and the centre-line edge, ahead of the anchor-foot knee [1]. In the middle, stone and body share the same line of push [1]. The broom is either across your back (30–35° to the target line) or parallel and flat on the ice [1]. The throwing arm stays extended, upper arm, forearm and wrist on one plane [1].
The handle is already in its pre-set position (10 or 2 o'clock) before you apply your hand [1]. Centre the index finger on the handle with a slight break in the wrist, and keep the pressure between 4 and 6 on a scale of 10 [1]. That is firm enough that it doesn't wobble, loose enough that it doesn't cramp.
Milestone: You stand the same way five times in a row, and a side photo shows shoulders and hips square to the target line.
Point your toe in the hack at the skip's broom, and let your hack knee and shoulders point there too [3]. The stone barely moves: for targets at the outside of the house it shifts at most about 2 inches (5 cm); mostly the body moves [1].
Turn the set-up into a ritual: foot, foot, knee, shoulders, stone, grip, always in the same order. Curling Canada describes the delivery as a simple movement where form follows function: the simpler it looks, the more automatic it runs, and you can focus on speed [1]. A ritual saves exactly that head space.
Right-handers throw from the hack left of the centre line, left-handers from the right one [2]. If you throw from the wrong hack, the stone is removed from play [2]. The broom hold and the position are otherwise identical.
The heel of the sliding foot is level with the toes of the anchor foot, both feet parallel with 2–3 inches (5–8 cm) between them [1]. Your weight sits about 50% on each foot [1]. That keeps the body calm and the hips square to the target.
Between the middle of the hack and the centre-line edge, ahead of the anchor-foot knee [1]. Many find the middle easier because stone and body then share the same line of push [1]. Try both, then stay consistent with one position.
According to Curling Canada, grip pressure is between 4 and 6 on a scale of 1 to 10, depending on the weight of the shot [1]. The index finger sits centred on the handle with a slight break in the wrist [1]. Firm enough for control, loose enough for feel.
The Drive in Curling: Backswing and Push-off from the Hack