This list of 'things to do' is useful not only when you are part of an active Co-Op Job but whenever your Farm has the ability to trade Bushels at a Market Stall or more than one Market Stall.
First of all, it always is beneficial to have a Neighbour who is willing to work as an unofficial partner to grow Crops that you need for your chosen Craft. Unfortunately, you are limited to three Bushels from any specific Neighbour's Market Stalls, but you can choose Bushels from more than one Crop or all three from a single Crop. There is a little trick to this if you have a Neighbour with the same Craft that you have. When you have chosen three Bushels from any Neighbour's Market, you have the option to 'Share' a Bushel of the same type as the one chosen last. If you have taken more than one type of Bushel, always save the one that your Neighbour needs as the last to take, so that you will be able to Share one of those with him/her.
Before you begin to take Bushels from Neighbours or the Game Feed, look at your own inventory to make certain that you have sufficient space to store them. You are restricted to 100 Bushels irrespective of the number of Market Stalls that you own. You are limited to five Market Stalls, moreover. Whenever you find a Bushel for any Crop, it automatically will be displayed at one of your Market Stalls, unless all of them are displaying a different Crop. You therefore need to make certain that you have a Closed Market Stall or one that offers the same Crop BEFORE you begin to harvest any Crops, especially if the Crops you are going to harvest are a variety that you or your Neighbour needs. If necessary, shut a Market Stall in order to give yourself a venue for the Crop you are about to Harvest.
The next step to take BEFORE you harvest any Crop is to go to your Bushel inventory (accessed either through any of your Market Stalls or through your Crafting Building) to 'Use' a Bushel of the same Crop so that you will earn more Mastery points for that Crop.
The following appear to increase your chances of obtaining Bushels when you harvest your Crops:
You can fertilise your own Crops using 'Fertilise All', a wonderful reward given randomly when you visit your Neighbours' farms or you can ask Friends and Neighbours to fertilise your Crops for you.
2. Crop Mastery
You earn Stars that represent the three Crop Mastery Levels for any Crop by harvesting specific totals of that Crop. There are three Levels and the higher your own Level, the better the chance of obtaining Bushels. With three Mastery Stars, for example, you are likely to obtain at least 4 Bushels when harvesting only 12 or 16 squares of the Crop. With no Crop Mastery, you may not obtain a single Bushel even when harvesting 100 squares. Crop Mastery is something you can begin to earn at Level 10. My post on preparing for Level 25 discusses the advantages of choosing a Craft before you actually are able to embark upon any crafting career. Go to your Inventory before you Harvest any Crop, therefore, to 'Use' a Bushel to increase the Crop Mastery Points gained from the Harvest of each square of that Crop.
Bees certainly are necessary for pollination of Crops, allowing you to unlock temporary pollinated Crops at the Marketplace. I believe that they improve the chances of obtaining Bushels as well, although I could be mistaken about this.
Although Co-Op Jobs do not require any Bushels or any specific Crop Mastery Level, it always is best to combine goals in Farmville and take a Job that will net you the Bushels you personally need for your chosen Craft.
There is a trick with respect to any Co-Op Job that can give you a good jump on the achievement of the requirement of total number of Bushels. This was taught to me by an old Harvest Moon friend of mine. What you do is plant almost your entire field with one or more of the Crops needed for the Co-Op Job you intend to Start/Join. Leave at least eight squares tilled but vacant!
When the Crops are fully mature, Start/Join the Co-op Job and then, BEFORE you harvest any of the ripened Crops, plant the squares that remain vacant with the same Crop. Once you have planted new seeds in the eight to twelve squares that you kept vacant, you can harvest the SAME NUMBER of ripened Crops. Do not harvest more Crops than you seeded, however, as they will not be counted towards the Co-Op total.
You see, you can trick the game into believing that the ripened Crops were planted during the course of the Job only if you seed an equivalent number of squares BEFORE you harvest the others. It is a little tedious perhaps, because you must alternate between Harvester, Tractor and Seeder again and again unless you have the new Combine machine but it can be worth the effort. After this initial cheat, you will be able to harvest the entire field the next time the Crops mature, obviously. It is only the initial harvest that has to be counted carefully.
'Fertilise All' will fertilise every tilled square on your field, whether or not Crops have been planted and even when Crops are fully mature. DO NOT WASTE YOUR FERTILISE ALL! Study your field before you use the item. If any of the Crops have been fertilised, harvest them and re-till the squares before you use the 'Fertilise All'. This is an important tip but easy to forget when one is involved in any harvest.