Undesirable behaviour from our children is much more obvious than desirable behaviour. Hence we are more likely to notice when they are misbehaving than when they are behaving well, thus, a child is likely to receive much more attention from their parents/carers for behaving badly than for when they behave well. This can lead them to repeat the undesirable behaviour because it gets them noticed by you.
It can be useful to redress the balance - try to 'catch your child doing something good'! Look for opportunities to offer praise and encouragement when they are exhibiting desirable behaviour - things you would like them to repeat. Look for small achievements as well as large ones and times when your child/young person has demonstrated effort even if they have not yet achieved some final goal.
Receiving praise is likely to make your child/young person feel good and nurture their self-esteem and confidence. I read once that children need at least 5 times as many compliments as criticisms. Building self-esteem and confidence is important for everyone especially children and young people and most of all those with additional needs who have to take extra "knocks" when growing up.
Some people worry that praising their children will lead them to be over-confident or conceited; however I would suggest that it is more of a risk to give a child too little praise, rather than too much.