If you only drive a limited number of miles each year, inform your insurance company of your typical yearly mileage they may give you a lower quote.
If your van does not have an approved immobiliser fitted compare prices for vans that have fitted and unfitted. It might be cheaper to have one fitted than pay a higher premium.
You can reduce payments by offering a voluntary excess, but keep in mind not to offer a huge sum as you will need to meet it if you make a claim.
You should declare that you van is for business when filling in your van insurance enquiry form.