Check the available room
Before choosing a tuck, put the shirt and trousers or skirt on together. The waistband needs to fit with the shirt inside it. If it is already tight without the added fabric, a more elaborate folding technique will not make the combination comfortable.
Consider the shirt's length and thickness. A long, crisp shirt has more material to accommodate than a short, soft one. Pockets, pleats and a heavy placket can add bulk in specific places. The most useful tuck is the one that works with those details rather than trying to hide them all.
Try a complete tuck first
Place the shirt inside the waistband without pulling it taut, then raise your arms gently and let a little fabric release. Sit down and stand again. The shirt needs enough allowance to move, but not so much that it forms a large fold you dislike around the waist.
Look at the side and back. Smoothing only the front can push all the excess fabric elsewhere. If the shirt keeps ballooning at the back, try distributing it more evenly or choose a looser waistband. Avoid fastening the trousers so tightly that the shirt cannot move at all.
Use a partial tuck with a purpose
A small front tuck reveals part of the waistband while leaving the rest of the shirt loose. It can work when a full tuck creates too much bulk. Keep the amount modest at first and let the side seams fall naturally.
Watch the line of the buttons. If the tuck drags the placket sideways, it may look and feel strained. A shirt with a very long curved hem can also hang differently at the back than you expect. Check that view before deciding the partial tuck has solved the whole outfit.
A side tuck makes a more asymmetrical line. Try it only if you like that effect, not because it is supposed to make every outfit more interesting. Some shirts are easier and more comfortable simply left untucked.
Let sitting be the deciding test
Spend a few minutes in a chair, leaning forward as you would at a desk or table. If the shirt pulls out entirely or the waistband digs in, change the arrangement. A tuck that needs resetting after every ordinary movement is not doing much for you.
Belts can hold trousers in place, but they do not remove excess fabric. Add one for fit or for the line it creates, then check the seated comfort again. The goal is an arrangement you can mostly forget once you leave the mirror.
