RHS guidance
Pruning is rarely needed in the first two years, just remove any crossing or misplaced branches. After that, prune at any time during the dormant season (November to March), but ideally in late February or early March when fruit buds can easily be distinguished from leaf buds. Fat buds produce flowers and fruit, while smaller, flatter buds form shoots and leaves.
A mature bush should contain about one-third old, one-third middle-aged and one-third young stems.
Prune out:
1.Dead, diseased, dying, weak, rubbing or damaged stems, plus any that are touching the ground
2.Twiggy growth at the ends of the branches that fruited last year, cutting back to a low strong, upward-facing bud or branch
3.Remove up to a quarter of the oldest and thickest stems at the base of a mature plant or prune to a younger strong shoot lower down on the branch