using tab to enter field?

I’m trying to access a text input browser field in a page of an application that has no script support
I tried to use the keystroke tab 19 times which enters me into the field that I can enter text

delay 30
	repeat with i from 1 to 19
		tell application "System Events" to keystroke tab
	end repeat

The script isn’t that good since I’m using the delay to wait for the program to be ready and to use the tab button 19 times.
The 19th tab is a box to type in, the 20th is a button that says “Browse”. I could also move back 6 tabs from the place the computer leaves you from the last command if there was a way to make the tab move backwards instead of forwards. How do I improve this script.