first you need to know if your chem of selection for dilution is soluable in the type of solvent you have )polar/no-polar/or slightly) both ethanol wich is what you will be using is slightly both , then the next step is how many mgs of this substance can bedissoved into a said amount od ehtanol, you can disolve thousands of milligrams into 1 fluid ounce of water or any other liquid depending on chem. but for what you are trying to do, lets say:
500mg/500milliters of ethanol, if pure and actually completly soluable you should have a liquid with 1mg per ml. cut that in half to 250ml thats 2mg to 1ml, if the substance is fully dissoved and weighed properly. by the way just because a vendor sent you "500mg" of a said chem, its more than likely alittle more or less, and sometimes alot more, or a completly different chem. so be careful it sounds like your making your own smoking blends, you will be pissed if the substance is not soluable, plus harware grade acetone has trace lead an other dangerous heavy metals in it, so consumptiongrade ethanol, is more healthy but less effecient due to evaporation rate, hope this helps
"you can always ingest more of a chemical to reach desired effect, but never take back what you have already ingested"