In one of my previous writings I suggest you guys bring a pocket reader with you and read it whenever you have lesiure time outside such as riding on bus or in subway cabin, instead of browsing on your smart phone.  Here I would like to recommend a very useful pocket book to you: "A Pocket Style Manual", a real pocket-sized handbook that is suitable for carrying it in your pocket of pants or jacket. 

What is the book all about?  It is an English grammar book which used to be my  daughter's textbook(or an extra-curricular book) when she was in college or in high school.  Concise, explanatory, not stilted at all, it is a grammar book serving as an entrance-levelled guide to lead you to better style and rhetoric in writing.  It's a Bedford Books, Boston, written by Diana Hacker, on which I've throughly read twice.  It's helped me a lot, and I almost always bring it with me when I am out on bus or subway, and I'll randomly turn to any page to read at.  You know, such kind of reading could also produce a sleep-inducing effect, and sometimes it would make me nod a little bit. 

Of course the book is not the only option to you.  You could have other favorite pocket readers of your own, or you could read electronic book while you are on bus or in subway cabin.  The point is reading will definitely benefit you much more than that of playing games or lineing stupid photos.  

P.S. I don't know whether the book is still available, nor do I know it has had  electronic copy or not.