Here is another thread which asked a similar question:
I think the responses in there might also be helpful.
My response in that conversation was this:
Improving in reading takes just one thing: practice
I think figuring how best to motivate and stimulate that practice is the key.
For some people, playing games works better, since the competitive context of the game might give them extra motivation to try to read and think deeper in order to beat their opponent.
For others, doing problems may be more effective, if solving problems outside of time and competitive pressures is more effective for them to learn.
For many, probably doing a mix of both helps.