I believed the ChessMentor helped me most as she lets me learn the tactics in themtic way and give interactive endgame training. Also the tactic trainer is useful if one can adapt to the questions requiring real-game-like decision making.

And in the last few days I studied common lines of my opening by viewing about 30 games for each mainline so as to get a general overview of the ideas and plans of the line. This not only acts as a compasses for the navigation of complex midgame but also a spotlight for the expedition against the sidelines given by your cunning opponent.

Once you know the true motive of the main move for each side, you can spot out the consequence of the deviation in set-up. Practical action can then be taken to manipulate the possible result of your rival's last move. Structual weakness, loss of tempo or even immediate tactics could be seen. Actually, studing an opening's concept in deep can enhance stragetical thinking.

Hope this help:)

Congratulations! Can you name a specific factor which has enhanced your playing strength?

I don't play turn-based, but in online "live" blitz on various servers I was 1600+ only as a kind of rating peak, each. Difficult, if not impossible to maintain for me nowadays. I'm happy if I can stay 1500+. But I don't do any regular training or studies anymore, that's probably why.