Train tactics.
Yes. Absolutely yes.
However.
I've just checked NimzoIndy's profile, and it seems like that he does not like to calculate anything. There are a lot of puzzles where he gives the wrong answer after "thinking" for 6 or even (gasp) 3 seconds. In my opinion, 3 seconds isn't even enough to count the material, let alone properly solve the puzzle.
This is not good. Banging out moves will not help anyone to improve.
And you also can't expect to keep improving relying on digital tools only. You can't have a phone around all the time. Make sure to have some good books as well. Nimzowitsch's "Chess praxis" is very good, as is anything by Jerry Silman.
"How to become a candidate master" by Dunne can help you even if you're not anywhere near class A.
Logical Chess by Chernev doesn't have a single bad review as far as i can see, except that some analysis may be outdated.
What does you mean with your "analysis may be "outdated"?
How can it be... if some analysis is right?
Well, outdated as in, if you look through it with an engine, he gives some incorrect evaluations, but they aren't significant enough to actually matter. The important thing is that you learn how to think from the book.
It was written in the mid-1900s I believe, and was just constantly reprinted.