It doesn't mean much without context. But I'd guess it's about writing. Don't put words in your writing that don't mean anything. Don't pad your writing, etc.
"Make every word tell" is BrE in my opinion. In AmE we would say "make every word count." To employ another AmE idiom, it means don't waste a single word, i.e. even one word. Each and every one of your words should carry its own impact.
Yes, it's a bit of an odd collocation. 'Make every word/bullet/second...' usually, in my experience, ends '...count'. Perhaps 'tell' is an unlikely choice in either Br Eng or Am Eng, and it found itself in the forefront of the writer's mind because of the pun. I've seen some psychology texts about this sort of pre-loading of possibly appropriate words.... No reference, I'm afraid, but perhaps someone else can help:-?