1. Don't start your book by introducing two major characters whose names start with the same letter. I don't care what rationalizations there are for this, just DON'T DO IT. Given, there are only twenty-six letters in the alphabet, and at some point you may have to bring a Thomas and a Thad onscreen at the same time, but wait at least fifty pages before doing so. By that time your readers will have a handle on who Thad is and won't be stopped every time the two characters are speaking to each other, trying to figure out which one is which.
2. Keep your chapters short. At the very least, unless your book is under 60k or so, have chapters. To you this may be an aesthetic question, but to your readers it is a question of readability. Few people have the leisure to sit and read for long uninterrupted stretches, and chapter breaks are the sensible point for them to put the book down for a while without losing the thread of the story; make that concession to a reader's time and they will be favorably disposed towards you. There's also an argument that shorter chapters with well-constructed breaks may lead readers to read more at a sitting. Take a look at thrillers--I mean, don't go the James Patterson route and slip in a bunch of one-page chapters essentially as lazy punctuation, but have some respect for the reader's time and sanity.