Midgame

Many books have been written which try to answer "how to play the middlegame" so it's hard to sum up in a forum post, but this is pretty much how it is...

It's all about piece activity. By piece activity I mean your non-pawns are attacking and defending important points.

In slower moving games "important points" are typically weak pawns or an unsafe king. In faster moving games they're typically undefended pieces (or other pieces subject to simple tactics, which can also include the king).

As the opening ends if the pawn structure is locked, then to get active pieces you'll most often need to play what's called a pawn break. Pawn breaks force some pawns off the board, which opens files, ranks, and diagonals... those open lines is how your pieces will eventually get active.

If the pawn structure is not locked then you can try to get active immediately e.g. by attacking their king (if it's vulnerable).

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That's the idea of it. For practical tips you usually seek play (meaning seek to have active pieces) primarily on one side of the board... yes a common technique is alternating attacks on two sides, but that's only after you've tied down your opponent with your initial thrust. So early in the middlegame players usually seek play in the area (kingside, center, or queenside) where they have more space, more non-pawns, or both. By space I mean the squares behind your pawns... this leads to the tip "attack in the direction your pawns point."

For example in the position below, white's natural play is on the kingside and black's is on the queenside.

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In the example below, it's natural for white to attack on the kingside because black only has 1 defender on that side of the board (their rook on f8)

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So to recap, in the middlegame you want active pieces. Pieces are "active" when they're in contact with weaknesses. Weaknesses are weak pawns, undefended pieces, or a vulnerable king. In the early mid game you try to get active pieces by seeking play in the area where you have a natural advantage. A natural advantage is having more space, or more raw force.

And I guess it's worth mentioning that some positions are very balanced. Sometimes neither player can realistically hope to have an advantage for themselves on any area of the board (kingside, center, or queenside). In cases like these you'll typically just make small improvements. Knights on outposts, rooks on open files, that sort of thing. Notice that a piece that is very mobile and centralized has a greater probability of being active some point later.

And if you're very new you may not know that weak pawns are doubled, isolated, or backward (those are chess terms, e.g. google "backward pawn" if you've never heard of it).

And when I say "tactics" I mean for example forks, pins, skewers, removing the defender, and discovered attacks... these are common tactical themes, and actually there are a few dozen names (x-ray, clearance sacrifice, etc) in fact way too many for a new player to bother with, but anyway, more things for you to google if you're truly new.

I’m not really new, just play like it. Your post is good advice and thank you for giving it!