A BAS can be made up of the net GST you’ve collected, the taxes you owe for your employees you withheld and a portion of taxes you owe for your entity.
GST withheld is a byproduct of your sales and purchases. So long as you are recording these correctly, the amount you are legally required to remit is something that you have effectively collected on behalf of the ATO so it is not necessarily something that can be reduced. The thing to remember is if you ordinarily collect GST on your income, but seem to be entitled to a refund each quarter, you may not be making any profit at all and should have a consultation for that outcome before it becomes too late.
PAYG withheld from your employees is a byproduct of how many people you employ and the amount you have to legally withhold, so it may be difficult to have this reduced. But this is not your taxes, but monies owed for others.
The only taxes that you would pay on your BAS that belong to you is any PAYG Instalments that the ATO raise for you to pay. It is recommended that these amounts are reviewed regularly so you don’t overpay as you go, but also if you are underpaying, you are preparing to save for those taxes that will be due once the final return is lodged.
If you feel you are paying too much on each BAS, then organise a consultation to have your BAS reviewed. It has happened to others without them realising.