Would the series of dilutions be
1 ml of stuff in 10 ml of water (distilled)
1 ml of stuff in 100 ml of water (distilled)
1 ml of stuff in 1000 ml of water (distilled)
Can be, doesn't have to be. 1:2, 1:4, 1:8, 1:16 makes sense as well, or 1:5, :25, 1:125 and so on. Actually you don't even hot follow any easy to reproduce pattern, 1:5, 1:30, 1:123 would do as well. What matters is that you know what you did, you cover the range and you plot the results correctly.