Growing scripts: where to get help for memory problems

As my scripts go big and bigger memory is insufficient. I found it is not so easy to expan the possibilities with other scripts (llMessageLinked) or using notecards for storing data. It's possible, there would have been less troubles, if I would have been thinking about at start, but thats not the case
I was trying to find some useful solutions and find to my astnoshement only very view informations about good possibilities for finding such solutions. As I am not a very experienced programmer I would be glad for a place, where others explain approches to these problems that have been useful.

A good thing could be to put some big functions or code parts in another script. But big functions, if not very well designed from start, contain global varbiables. So you end up with a lot of code for sharing these values.
I also thought about changing my code in a way, that some existing variables (string variables for example) get stored in another script, with llMessageLinked. I imagined, I could substitute the variable in the script by a function that stores/gives back the value to/from another (new) script, used as storage place. This would prevent big changes to the original script. But I did not find a way to implement this.

Does anyone know a text, where these things are discussed?