Eye contact:
If you need your child’s attention, look him/her in the eyes and give the necessary instruction when you are sure you have his/her attention. You will be far more successful in getting the outcome you want.  Ask them to repeat the instructions to ensure they have listened to you.
Move:
Movement is one of the best regulators for the brain and helps to regain focus and attention. Let your child go fetch something, stand up and stretch or do a few jumps when concentration is starting to dwindle to fuel the brain again.
Put something in your mouth:
Chewing on an apple, carrot, rice cake or popcorn are healthy versions to use the mouth and crunchy chewing action to gain focus and attention. It however might drive you mad if you are auditory sensitive as you will be irritated by the chewing sounds. Chewing gum also works well, but sugars, colourants and preservatives are contra-indicative for good concentration.
Check your environment:
Reduce external noise and distractions to ensure the environment will make it easier not harder for your child to focus.