I don’t know if you have problems with it. But I write too long sentence when I write a longer text. However, for a fluently reading flow I need more short than longer sentence. But this can’t be anything. (I know simple words must be there, too.) What are your best tips to get a reading flow where even reluctant reader gets tears?
In addition to what Bufty said (it really does take practice, and studying how other writers do it can also be helpful), one practical tip I can offer is to vary the length of your sentences. Think in terms of balance: balance long sentences with short ones, and very long ones with very short ones. Use medium-length sentences (and even those should vary somewhat in length) to fill in the bulk of the narrative. That's one aspect of good flow.
Another has to do with the logical reveal of information. The contents of each sentence must logically connect to the contents of the next sentence. If there's a break in the connection, it should be because the subject has changed or the story camera is pointed in a new direction. Ideally, it will feel natural when that happens and not jarring. Starting a new paragraph with new information can help with that transition.
You always want to give the reader the feeling that the narrative and dialogue are building toward something. It can often be effective to put the most tense, interesting, or surprising word or phrase at the end of a sentence of paragraph.
Last, study the uses of rhetorical devices. These can add power and eloquence to your writing, which will put you on the road to tearful readers.
Here's a partial list. Also check out
The Elements of Eloquence by Mark Forsyth, which is both an informative and entertaining read.