Waste is basically just inefficient use of resources, and the first step to reducing waste is to measure it. That way you can make sure that each waste type goes to the best destination i.e. not landfill!
Most businesses start their waste reduction efforts by looking at the types of waste that they pay operators to take and dispose of, and estimating quantities based on things like bin size, and pickup frequency. But the best way to measure your business’ waste is to conduct regular waste audits - there are many businesses who can help with this. And don’t forget to apply the waste hierarchy to your work - the best options to reduce waste are to only use things you need, and to reuse them as many times as possible.
If you design or source the products you sell to your customers it is still worth thinking about the waste associated with the manufacturing processes that occur at supplier level. There are design tools available to help you assess how much waste there is per product you bring to market, and to design products to be durable, and easy to recycle and repair.