When writing, how do you avoid starting every sentence with 'i' or 'he' or 'the' etc ?

This is a huge problem I have. I always seem to fall into this 'hole' when I really get into the flow of writing and all my sentences end up starting the same. I have to stop writing and go back and change it all. How can I avoid doing this? Do you have any tips? :) ps: sorry about any spelling mistakes or something. I'm on my phone and the auto-correct hasn't been very successful :P