One of the biggest problems using spray glue for upholstery is keeping the glue off the visible side of the material. Once you get a drop or mist of glue on there all the cleaning in the world will be of little help. You'll ultimately end up with a spot that collects dirt and grime and shows up to mar your otherwise perfect upholstery job.
To combat this problem, always keep scrap sheets of printer paper next to the workbench. You can surround the flaps of material that you are spraying with the sheets of paper. They are stiff enough to slide underneath and light enough not to slip away. Use each piece of paper once and then throw it away. Any residual glue will transfer from it to your upholstery fabric.