If I don't think the roads will be well marked then I tend to just go by the incremental mileage to the next turn and ignore the total miles anyway. So let's say the sheet says to turn on 'A' St. at mileage 35.4 followed by a turn on Elm at 39.6. The difference is 4.2 miles, so as I make the turn onto A St. I note the mileage on my odometer, add 4.2 to that and then start looking for Elm street when the odometer gets close to that value.

That way it doesn't matter if my odometer has any extra miles because I rode from home or took a detour along the way, got lost, or whatever.