Yeah, chess is so easy you can drastically increase your rating in a very short period of time with no work.
I'm going to be world champion. I'm playing Carlsen on Friday. I trained back rank mates for 2 weeks.

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Other than chess.com, what other resources - preferably free - could you use to drastically increase your play in a very short amount of time?
It would also be very helpful if they could be centered around learning and getting better at spotting various tactical ideas.