Tactics and very basic endgames.
Skip openings and strategy.
Just my view ... I wasted 100s of hours on openings, and strategy is something that's more ephemeral and harder to grasp than tactics.
Tactics, tactics, tactics, until you're 1800. But you must know how to mate with Q, or R, and how to queen a pawn with K+P vs K.
That'd be enough till 1400.
Tactics, Endgames, Openings, and then Strategy. Strategy really isn't that important for your skill level, wait until you're around 1700-1800. As for openings, also not that important, find four you like, 2 White and 2 Black, and learn a few variations. Tactics will always be important, and Endgames just as much as Tactics. The others, don't worry about them.
study tactics first, then basic opening theory,endgame last
Tactics first. Everything else is based on tactics.
You should learn a little bit from each of them. The only one you can somehow neglect is the opening theory, but still you must know the basic opening principles. And if you play e4/e5 you should know how to answer king's gambit and the two knights (Ng5 variation). At least.
#1 -Endgame
then Tactics
Openings
Strategy
but don't ignore the others for any one of them
strategy...tactics...
the same?
99% Tactics...Until you are around 2000 USCF you should focus mainly on tactics. Gaining a small advantage in the opening or having a vast endgame knowledge will be of no benefit to you if you drop a piece to a three move combo in the middlegame and reach the endgame material down. Most games under 2200 USCF are decided by tactics.
Openings set the stage for tactics in the midgame. Exploitation through tactics is definitely guided by strategy in the soundness or unsoundness in the opening. Many tactical opportunities are created by weaknesses that result from poor strategy. Conversely avoiding weaknesses, blunders, and mistakes are the best tactics of all. As for the endgame, no matter how brillant you are, especially when you are less brillant than your opponent you still have to finish them off. Tactics are a very important means but if your overall game lacks, it won't always bail you out. Generals command soldiers, not the other way around
Seems like,after looking around,lots think tactics is the answer. For want of a nail a kingdom is lost!
Get a very good grasp of opening and middlegame principles. Be comfortably familiar with your few major openings of choice. Know good pawn structure from bad.
Work on tactics a lot. A lot.
Know how to play K+P v. K, K+R v. K endings, and of course know how to mate with a queen, a rook.
....................................
Do all of the above as your course of study until no less than 1600 USCF, higher being reasonable too. Don't just pick one thing. Do 'em all and you will not only get stronger you won't get bored.
At some later point if you find yourself in very even games with opponents your strength (and + c. 200) then some time spent on postional play would be in order, such as what makes a good/bad bishop, b v. n, weak/strong square complexes. This would be something you work up to.
What is 1800 USCF? Well, it's not 1800 CC Chess.com. While it's a slippery question, perhaps subtract 400 from chess.com for an equivalency of "chess strength/knowledge." If you're not playing official OTB, following guidelines for a USCF 1800 may be like a 2000 or 2200 or more here. Just something to keep in mind.
tactics mainly, they're also fun to study so its easy to spend more time on them. i think endgame is very important, knowing how to draw a lost game, win a a drawn game and finish winning what should be won (if that makes any sense). openings basics are a must, you dont need to study variations and novelties, but basic ideas behind a few select openings that you like to work with. I believe Rubin Fine's books, his endgame and opening books, are great reads. strategy definitely an ethereal amorpheus topic that cannot be ignored though, a bad plan is better than no plan....
Make sure you know your basic endings: queen checkmate, rook checkmate, K+P vs K, K+R+P vs K+R (just basics like Lucena & Philidor). Learn opening principles--but hold off on intensive opening or strategic study for now. Mostly focus on tactics.
strategy...tactics...
the same?
No...
Tactics is best described as a single or brief series of moves that give you a material advantage as a result.
Strategy is an abstract concept that you choose at the beginning (or at a critical juncture) of the game when you decide what set of tactics would best defeat an opponent or their choice of opening. e.g., "In an open position, preserve your bishop pair while killing off your opponent's bishops."
#1 is endgame for sure. Study the 50 or so most common checkmates so you can identify a winning condition quickly.
One of the saddest consequences of using computers to study Chess is that many people have lost the talent to spot mating combinations, since we become used to engines being able to do it for us. 
Games that used to be over quickly now turn into drawish marathons as both sides struggle to find a win.
Given the following topics:
Strategy
Tactics
Endgame
Openings
In what order do you think these should be addressed as a 1200 to 1400 rated player?