I don’t know where I’m lacking

No one needs to look at your games, all 546 rated players lack the same things.  No shame in that, we all start at roughly the same spot. 

Anyway, in my experience for a player of that rating, the two biggies are:  (1) ability to spot blunders by either side; and (2) basic beginner principles.  In the one game I looked at, your last one, it was pretty much exclusively the blunders, but I'm confident that you could also use help with the basic principles just by the rating.  

Practicing tactics, and playing a long enough time control to have a thorough thought process for every move, are very useful.  By taking the time to have a thorough thought process and consider all checks, captures and the like for both sides every move, you can train yourself to do it, and eventually do it in quicker play.  

Your welcome.  Its also good to post a single game, and learn how to stick the game board with the moves directly in your post.  Preferably pick one you lost that was hard fought and not just decided by an early blunder.  More likely we'll be able to help you with some of the beginner principles you missed that way.  Its also useful to let the computer show you your blunders.  I'm happy to explain beginner principles, but feel like folks should be able to discover the simple blunders themselves.  Its another thing if you consult the computer and can't figure out what its trying to tell you.  

Yes, you did develop fast in the game I looked at.  Developing fast and castling is one of the big ones.  There are a lot of others, I won't even try to do them all, but here is a quick list for you:

(1) develop fast and castle early;

(2) try not to move the same piece twice in the opening without a good reason;

(3) don't move the pawns in front of where your king is going to end up without a good reason, as its often weakening;

(4) "a knight on the rim is dim" is a stupid sounding ryme taught to beginners which relates to the fact that on the rim your knight has fewer possible moves, and thus fewer squares it controls.  It generally does less.  Absent a specific reason, its not an optimal place for a knight;

(5)  Don't take your queen out too early.  She often just becomes a target and the other side can get free developing moves by attacking her.

That sort of thing.  Some of them its most helpful to explain in the context of a game.  And some of them are typically hard for folks in your rating range to digest.  For example, we teach about doubled pawns and isolated pawns which are generally a negative, and beginners then get way to focused on those issues.  Other things are maybe better called common beginner mistakes than beginner principles.  Like one thing I see all the time is that someone attacks one of a beginners pieces, they will 90% of the time attack one of the enemies pieces rather than protecting, moving or trading the attacked piece.  Of course, sometimes ignoring a threat and making one of your own is the best move, but beginners do it all the time as a matter of course, and it causes them to make a lot of mistakes.  

Took a look at some games briefly, mostly:

- tactics

- ask yourself what your opponent is threatening next move

My suggestions to beginners are always "1. Try not to hang pieces. 2. Keep the pieces coordinated and close to each other in way that defends each other. Always make sure everything is defended."