You reported that you are struggling with your child wanting
things you do not want him/her to have. Try to offer an alternative
quickly when your child wants something that is not okay. If the
main situation of demanding is in stores, plan ahead to buy something
acceptable (or bring something) at the beginning of shopping. A small,
weekly allowance from which the child can purchase what they want
helps teach budgeting and reduces begging. Alternatively, be clear
that nothing is going to be bought, do not continue to discuss
it and do not give in.
When your child really wants something, instead of immediately saying no;
it works best to first spend time clearly stating that you know how
much he/she wants the thing in question. When the child calms
somewhat by feeling understood then you can offer another time or
another thing that might work. For example, doing the thing s/he
wants during the child's 'special time'.