It's funny - I've been playing this game across editions for nearly 40 years and ... I can think of very little that I bring from earlier editions into my current games that are tied to those editions and not to setting elements that wend their way into whatever campaign setting I run games in.
So from B/X D&D I bring the idea that "gods" such as they are aren't the only source for clerics/paladins to get spells - you can also devote yourself to a philosophy such as Law or Chaos or Balance (or many others now as that idea has refined itself over the decades that I've played the game) and you receive spells just like clerics who devote themselves to gods or fiends do. In some campaigns the "gods" aren't even the ultimate source of divine power, just one of many intermediaries between humanity and that divine power source.
From 3e I bring the use of minis in combat. We never used them before 3e and they've been a constant since, whether it makes sense to use them or not.
I enjoyed 4e a lot - but I don't use a lot of it in 5e. I use the bloodied condition like other folks on this thread - mostly because my players use it, and also being able to communicate to them that they're making progress in the battle turns out to be narratively useful. I build more interesting battles than I did in 3e, but since 5e isn't a wargame it's more for the narrative than it is for the challenge. (It's really interesting how many mechanics from 4e make their way into 5e and yet how different the two games play - how combat in 4e is the core of the game and how in 5e it's just kind of one element of the game, and not even usually the most interesting one IME).
I think I bring a lot more from other non-D&D games into D&D. My adventure pacing owes more to the Torg and Marvel campaigns I ran in High School than to the D&D games I ran, and my DMing style probably owes more to not just Torg and Marvel but also the Ars Magica and White Wolf games I played in college and the GMs that I picked up tips from than to D&D.
