The way I'd do it is to double the amount of propanone and H+ ions in the solution. You can then work out the rate of the overall reaction from the concentration change of iodine in the solution. If the rate doubles when the conc of your H+ or propanone doubles then they are 1st order etc..
I don't know how you can do a graph with respect to Propanone or H+ ions but I'm sure it's possible, you'd have to find a way to observe the concentration change of each...