Strategy

Efficiency

 * Look at the efficiency of assemblers to know why they are idling and try to reduce idling as much as possible.
 * Assemblers have different processing time, sometime you can queue assemblers (for each Fit Body you will have one Paint), sometime you should split them (build one Fit Electronics for almost all of your production line)

Local Supply stockpile
Try to build a Supply stockpile near Assemblers. Some Assemblers (such as the Fit Body or Fit Engine) will need one dedicated stockpile per assembler because of the quantity of ressources needed.

Supply stockpile will act as a buffer and should request resources upfront of the assemblers meaning you shouldn't have to wait for the Resource Importer

Reduce your expenses
- Open the "Financial Dept" window (by clicking on the money indicator on the upper-right of the screen) and try reducing your expenses.

Mainly, there is two you want to focus on :
 * Electricity : Research Power Plant
 * Raw Materials : Try building parts inhouse by researching assemblers starting by "Make"

Increase car price
- Increase the car (from the "Car Stock/Sales" menu) price by up to 75%. You will probably see some cars unsold, but they will be sold quite fast.