Generally, when you are using "this" to start a sentence, you are using it as an adjective describing which thing you are talking about (this cellphone, this plate, this car etc.), so be sure that when you do use "this" it is always with a noun and not "disembodied" as my grammar teacher used to say. Additionally, "this whatever" would generally be the subject of the sentence, so you can use most of the sentence starters in this article in front of it (or use a phrase that starts with one of those words) to vary your sentences.
There are a few other phrases that could be used instead of this:
1. The object in question.
2. The thing I was talking about.
3. The aforementioned item.
4. That object
You can also use a synonym for the item in question. For example, "this jacket" could also be "this coat." However, don't switch words just to be different because sometimes that can confuse the issue. If the "this..." item is the subject you are talking about, you can use "it" also. Here are some examples using the phase "this book."
This book is the one I have been wanting to read for over a month.
Moreover, this book is the one I've wanted to read for a month now.
For a month now, I've been wanting to read that book you just found.
Waiting for over a month, I finally found this book I've been looking for.