Well, to be honest, FTL is just a templating language for generating markup, and in this respect is practically identical in purpose to JSP, ASP, PHP, etc. So the usual techniques apply: factor out common parts (headers and footers being the most obvious examples) into reusable fragments that can be used through a straight <#include> or called using a <#macro>.
I'm not aware of any editor that has semantic awareness of FTL syntax, if that's what you're looking for. There's a Freemarker plugin for Eclipse that basically provides syntax highlighting and some code templating. It didn't work very well for me, at least not when I tried it a few months ago. (The syntax highlighting for ${expressions} didn't always seems to be in sync with what I was typing.)
(There's a Freemarker bundle for TextMate, which is what I use, but that only applies if you're on a Mac and it seems you're on Windows, since you mentioned Notepad++.)