I don't like doing most main goals, but I was able to do the last two in a row. Here is how I did it:
* Request appliance parts from neighbors as soon as the goal is announced and again at the beginning of each day (where a day begins at 12:01 Pacific Time) as early as possible because some of your neighbors might take up to 18 or even 20 hours to fulfill each request and because there is a maximum number of parts you can receive each day
* Ask slightly more than half your neighbors (e.g. A-M) for the appliance part you need more of (e.g. 28 or 40) at the beginning of each day and the rest of your neighbors (e.g. N-Z) for the other appliance part (e.g. 12 or 32) each day.
* Gift the goals parts to all your neighbors that do goals each day because some people will only send you gifts if you gift them first.
* Use Collectibles to build new appliances as soon as you have the 40 or 72 parts needed (combine gifts received, requests fulfilled, and parts produced via Collectibles).
* Be aggressive in building new appliances because more appliances produce way more collectibles, which lets you build at a much faster rate.
* Always be cooking, except for the 2 and 3 hour recipes while you sleep
* If falling short by one cook's worth, such as if you need to make 25 of something to complete one of the sub-goals and only have 24 made, consider using one to three gems to do the 25th, to speed things along, especially if it is the difference between being able to cook overnight vs not. Remember that you have up to 9.99 hours to serve a 5 hr recipe after you start cooking it, so it can totally be made overnight. Reasoning is that a total of say, four gems spent by the end of the 14 day goal is a small price to pay of you absolutely love and would be able to earn the $20K, $32K, and 65 gem items as a result!
* If using gems for this purpose, which you should only need to do once or max twice per 14 day goal, time your gem usage so that it finishes cooking after the hours remaining crosses an even-houred threshold (e.g. 2 hours remaining, 4 hours remaining, or 6 hours remaining). In general, I have found the best use of gems to be getting from the 3hr to the 5hr recipe and from the 7hr to the 10hr recipes.
* If you can complete the 5hr recipes before the new day starts at 12:01am Pacific Time, then you can request goal parts a day earlier and be allowed more parts for that appliance sooner.
I am sure I have more tips, but this is a really good start.