Here's a simple trick I've discovered recently.
It improves speed and also eliminates the flashing white windows we see in Windows.
I need to switch to a different table to do something and then return to the current layout. Being lazy I would select a pre-used layout say a Form or a report or table that I designed for a specific purpose. If the current layout is smaller, I always say a white flash as the other layout was used. So I thought to myself, I'm smart enough to solve this problem.
So what I evolved was the idea of using a layout at least the same size or smaller. For instance using a layout for an iPhone. This solved some of the problem.
Then I thought, lets use a blank layout to eliminate any slowness caused by elements on a layout. That also worked for doing something using a second table. Then I found that occasionally FileMaker DEMANDS that a field be on a layout. So I put that field outside the margins.
Summary: use a small layout with no fields when you have to change layouts do something quickly in a script and add the occasional obligatory field outside the layouts margins. Don't use layouts you've designed that have a dozen fields from related tables doing deep calculations.
This will not work in every condition as i am sure others will reply but when it does it improves your interface and speed quite noticeably.