Your topic sentence serves many purposes. It can set the tone for your piece, introduce both the subject and your opinions on the subject, as well as provide an outline for the writing to come. In a way, your topic sentence works as a map for the reader to follow as they travel into your piece.
I have been an avid writer for as long as I can remember, and I learned early-on the importance of a strong topic sentence, so here are a few things I learned along the way that will hopefully help you to be able to construct a clear and concise topic sentence.
First of all, keep it simple. Make sure to cover only what you plan on discussing in the paragraph to come. Avoid going off onto tangents that may be related to the topic in some way, but are not necessarily what you wish to expound upon in this particular piece. Use commas to set off any items in a list that you will later explain more thoroughly.
Giving examples of topic sentences is a little bit more difficult, but I can give you a couple. If you are writing about why you love Canada, for example, your topic sentence could be, "I love Canada for its amazing cuisine, breathtaking scenery, and diverse culture." If you are writing about a two-sided political issue, your topic sentence could be, "Many people believe we should do away with social-welfare programs, but there are a multitude of reasons why this would ultimately be detrimental to society."
Each of the example sentences lays out a map for both you and the reader. The sentences make it quite simple for you, the writer, to consciously write out supporting information, and the sentences prepare the reader for what is to come so that they can analyze and interpret your writing