For a 100% effective layout you need 4 iron buyers, 2 iron foundry and 1 seller.
Later as you research more technologies, these relationships change. For each component a chart shows how much of everything you need.
Depending on your upgrades, these numbers may be very odd, then use your best judgement to get the best layout :) (Like in other places you don't need good judgement :p)
Labs give huge bonus to research centers, so use them as many as you can afford if you want to research new more advanced technologies.
Luckily for you, setting up a lab can be quite a task. Labs require many different resources to be effective, but at the same time make production chain quite costly.
Plastic production is a bit more complicated, as it also produces Waste.
Resources come out clockwise starting from top left: plastic, waste, plastic, waste and so on. Using this piece of information, you can design your layout.
Later sorters will help to organize waste handling, additionally you can research clean production that will remove waste completely after you get electronics.
I found a bug
Why can't I get 100% efficiency for a buyer
Check that you actually transport everything out from buyer. Sometimes one exit conveyor is not enough.
Waste & plastic switched order
Upgrade is useless.
Some upgrades may seem useless at some points - just don't buy them yet - they will be useful later. It is wise to think which upgrades are good for you and which are not. For example sometimes buying 3 upgrades at once would mean you don't need to change your layout. But buying one of them would mean you have to redesign a lot.
If you bought an upgrade that changes production in a way you don't like, just sell it and all good.