Transition words are very important to organize your ideas. Think of your writing as a conversation between you and the reader. You want to make sure you clearly guide your reader through your writing piece. Transition words and phrases are key for that.
The tough part is varying the transition words you use. Don't be a next-aholic! Move past first, second, third. Varying your transitions will help to strengthen your writing. You all know how much I like sentence starters. Right up until I graduated from college, I always had my starters in front of me when I write. It's a great way to make sure I don't overuse my favorites. Writing that's the same all the time is boring! Shake it up!
This sheet of transition words and phrases will help you vary your writing and stay organized.
Furthermore, use it!!!