Getting from 1500 to 1800

Hi, I am now at ~1500 chess.com rating, and need to study more besides playing to keep improving. What lessons/courses at chess.com would you recommend at this level?

I can spot basic tactics and have a feel of where my pieces belong, but I am not consistent in my play, nor in my openings...

I was about to post a very similar question.  I'm a 1600-1700 level player right now, and I'm also looking for advice how to get to 1900.  

Do not use your rating as an indicator of how to improve, use your games.  A 1500 and a 2000 may both need to improve their calculation.  A different pair of players, also 1500 and 2000, may need to work on their endgame.  I know a GM who was told that he didn't calculate as well as other GMs and needed to work on his calculation (but his intuition was better than his peers).

Analyse your games.  Identify the common weaknesses.  Work with a focus on these areas.

That's helpful advice, but I'm looking at the same time for a little bit of structure.  Good books to read once you're advanced beyond patzer chess.  Good exercises, etc.

When I was playing seriously I enjoyed Kotov´s The art of the middle game.