Check out the "Go to Field" script step...there is a "Next Field" option.
There are a few different options as to how you use that script to get into that field...and it partly depends on the version of FM you are using.
So far I am unable to get the script to trigger when clicking on the second tab in my layout.
If I cntl-click the tab on my layout, and select 'Set Script' Triggers', I see OnObject Enter and 5 others. I've checked it, and set the script but it never gets to the script.
The script triggers if I set it to trigger on the first field and tab into it.
The question now becomes how to trigger a script when clicking a tab to change to it.