I would propose that December is a good time to formulate a marketing plan for 2018.
To start the plan, take your anticipated planted acres times your APH. Take that number times 70% and try to get that number of bushels forward contracted. Most people are happy with three pricing levels that would fill as prices rise. If all three levels get filled, your marketing problem could be that you have additional bushels to sell at a good price.
The corn market has good carry in it, while the wheat market has tremendous carry in. The soybean market has a modest carry in it. With carries all the way to next harvest, the new crop price levels are better than nearby prices by as much as 10% to 20%.
I would suggest the following:
1/3 new crop corn $3.50/bu, 1/3 at $3.80, 1/3 ar $4.00

1/3 new crop beans $9.20/bu, 1/3 at $9.60, 1/3 at $10.00

1/3 new crop wheat $3.90, 1/3 at $4.20, 1/3 at $4.50
For wheat, revisit the marketing plan April 1, 2018, for fall crops revisit the marketing plan August 1. If no sales have been made by these deadlines, either contract some grain, or put offers in at lower prices.
These are prices that could be obtained without a large rally. Also, many producers should be able to make a profit at these prices.
I saw this on Twitter lately, ” January soybeans at $10 is a thousand times better than bitcoin at $10,000.” As always, we need to stay focused on what is important.