mid game objective?

I mean, whole books have been written on only 1 or another aspect of the middlegame, so I'm not sure an answer to this fits well in a forum post size

That said, what comes to mind is you want to play a pawn break in the area of the board where you have an advantage is space, piece activity, or both. Queenside, center, or kingside.

So other than trying to be ahead in piece activity, space (and having a safe king) you want to play a pawn break to open lines for your pieces. If you can use those lines to infiltrate to your opponent's half of the board, your pieces will be a lot closer to targets like their king, weak pawns, or loose pieces. If you have more space in addition to this, then your invading forces have more room to maneuver, so the defenders wont be able to respond to all your potential threats.

Although, if you're losing a lot of games quickly, then it's probably all about tactics, and a habit of looking at forcing moves.

For example, imagine your candidate move as if it's been made on the board, and find the move from your opponent that you'd be most afraid of seeing (usually a check, capture, or threat). If you still like your move after finding the opponent most annoying reply, then go ahead and play it.

Yeah I'm in the habit of bringing out 1 or 2 pawns and then mostly minor pieces. I think that is my problem. But when i do bring out more pawns, thinks tend to go downhill =( and I lose them and then am in a bad position

If we're talking openings that's good, you should limit pawn moves.

Also in the middlegame, if you move a lot of pawns, it leaves behind a lot of weak squares the opponent may take advantage of.

When the center is locked, generally you'll pick a side (kingside or queenside) and go for that side only. Rarely can you play on both sides and get an advantage on both.

if I do pick a side and attack it, my opponents will figure out a way to attack my minor pieces that are in the middle (most likely a knight), which will disrupt my plan to attack.

One other thing that could happen is that if we're both playing defensively, neither of us can move a piece without it being taken or making a pointless sacrifice; This redirects me to the question of what do I do in the mid game, or in this situation specifically.

Sounds like you need to ask yourself, "what was the purpose of that move", every time your opponent makes a move, try to discern the opponent's plan too...then you can make moves to counter it....Steinitz is a good master to look at in this regard.

For example, if you have a space and piece advantage on the kingside, and the center is locked, it doesn't matter if you even tell your opponent exactly what you're planning to play, it will be impossible to defend.

Here's a common sacrifice example position:

Also I'm not sure you know what a pawn break is.

But if you have an example game you'd like to show where it felt like"neither of us can move a piece without it being taken or making a pointless sacrifice" then that would be useful.

In this game around move 9 or 10, none of my minor pieces can move without being taken, I am then stuck on what to do.

I'm looking at the position After 10...Ne7

The center is locked, and your space advantage is on the queenside (the d pawn is your lead center pawn). This might seem inconsequential, but it very often dictates which side of the board you'll be more successful on.

So your general aim in that position is to play the pawn break b4. Not immediately of course because that's a sacrifice, but just at some point in the future.

So your move 11.a3 was reasonable because already you might be able to play b4 next move.
However 12.Bb3 was not good because it's blocking your b pawn from advancing.

One good thing b4 does is it will open your b file for a rook. Another is it will probably open up your e3 bishop too.

Here's an example. These are not the best moves for black. I tried to play moves similar to the game, and moves I thought someone his rating might try, just to show how quickly white's pieces seem to come alive:

Yeah, that would have been good to mention, my bad.

The simplest answer is to take your opponent's pieces and put him in a bad position.

The way you do that is to evaluate the position and there are a number of books that discuss that in a number of ways from Jeremy Silman's "Imbalances" in How to Reassess Your Chess to Dan Heismans's list of six cases of where you should attack in ...The Best of Novice Nook it boils to knowing what to look for.  Learning all the tactical motifs you can makes recognizing weakness easier.  Understanding strategic concepts like Knight Outposts, Control of Open Files, Isolated Pawns, Good and Bad Bishops, Overprotection, Pawn Structure, and King Protection also helps guide you to developing a position where you have middlegame advantages.

My book recommendations would be Dan Heisman's Back to Basics: Tactics and Jeremy Silman's How to Reassess Your Chess.  Some people think Silman's book is meant for higher rated players but there are lots of principles you should absorb that are put in easy to understand form like: N's on the 4th rank are as good as Bishops, N's on the 5th rank are better than Bishops, N's on the 6th rank can be devastating.  Most of your times should be studying tactics including working tactics problems here and at chesstempo.com.