Beneath a jacket
Fasten the jacket and move your arms forwards. If the upper sleeves pull or knitwear gathers in the underarms, the combination is too tight even when it looks good worn open. A finer jumper may help, but it must still feel comfortable at the neck. Do not choose an uncomfortably close collar solely to accommodate the jacket.
An open blazer reveals a large panel of turtleneck fabric. Dark knitwear beneath a pale jacket emphasises that panel, while similar colours connect the two garments. Look at the lapels too. If they press against a tall, bulky collar, a lower turtleneck or a collarless jacket may sit more easily.
Beneath a dress
With a sleeveless dress, the armholes and neck create two distinct joins. A smooth, fairly close-fitting turtleneck is often easier to arrange underneath than loose knitwear. It should still allow movement. Sit down and check whether the dress catches across the stomach or back.
A dress with narrow sleeves of its own often leaves little room for another layer. Do not force the pairing if the sleeves twist around each other. An open shirt or jacket over the dress can provide the additional coverage you want without placing two tight sleeves together.
Collar height and jewellery
Fold the collar in a way that suits its construction and feels comfortable. Several tight folds create a thick ring that may sit differently beneath a coat than it does alone. If fabric around your neck bothers you, a different neckline is an ordinary alternative rather than a styling failure.
A necklace can rest over the knit, but it is optional. With pendants, check whether edges or fastenings catch the stitches. For the first comparison, the turtleneck, trousers or dress and shoes are enough. Only then decide whether the outfit actually needs another detail.
