It's never too late to plan for 2018.
Download this Excel spreadsheet that calculates what you need to win per precinct based on 2014 performance. If you didn't run for office, pick a candidate in a similar race and whose performance you except to match, e.g., if you're running for County Commission, pick a candidate similar to yourself that ran for that same office.
You'll need to update voter registration numbers up until 2018's close-of-book voter registration totals to get up-to-date numbers.
The spreadsheet automatically then automatically calculates the numbers you put in and gives you a running total per precinct on the far right.