Buy softer fabric clothes such as cotton and flannel.
If possible avoid polyester or other man made fabrics especially next to the skin.
Try to identify if the child is more comfortable in tight or loose clothes. If they prefer tighter clothes, then wearing a snug vest, T shirt, long johns etc under their clothes can help.
Wash new clothes a couple of times before your child wears them.
Use familiar laundry products and conditioner.
If the child has olfactory sensitivity avoids the use of strong smelling detergents or conditioners.
Remove any tags or labels on the clothes prior to asking your child to wear them as these can really irritate the skin and put the child off the garment.
Whenever possible use seamless undergarments or socks and tights, if this is not possible then turn the garments inside out so that the seam is on the outside.
Watch out for other irritants on clothes, i.e. Velcro fastenings next to the skin, elastic around the waist, scratchy backing on logos or patterns, tight collars or polo neck sweaters, elastic next to the skin etc.
Learn to compromise with the child i.e. if you wear your shirt and tie to school/ going out to dinner/family celebration etc then you can change into your comfortable clothes when you get home.
If possible match up something new or formal with a familiar comfortable item of clothes i.e. when going out allow the child to wear a comfortable shirt with a new/unfamiliar pants.
Whenever possible allow the child some choice/control over the type of clothes they wear. This may not always be appropriate with younger children and sometimes compromise needs to be used.
If child is particularly intolerant to school shirts/pants or dislikes wearing a jumper, explain their difficulties to the school staff and encourage them to agree to let your child wear polo shirts/sweat pants etc, items that they are more comfortable in. After all it is more important that your child can attend to lessons than to be distracted.