That is a very interesting question. Most people simply do both at the same encounter to save.If you have the luxury of doing them separately, start with botox, allow at least one week for effect and then do the filler. This is only relevant if you are injecting the product into the same anatomic area for example the glabella. If you are injecting botox into the forehead or glabella and filler to the lower face then it probably makes no difference. Enjoy the products.
I often combine both in the same visit. If, however, you want to see the effects of one before the other, you do the Botox first and schedule your fillers a couple weeks later. This would be if you are placing both products in the same region (e.g. frown lines)