I learned a huge lesson in using the tab button on my laptop when starting a new paragraph. My normal habit when writing is to hit enter to move to a new line and then tab once to place my cursor at the preset shift for the stating of a new paragraph. I never knew that this also carried over spaces, cleverly hidden between the left index line of the page and the end of the insert for each paragraph. This became painfully obvious when I uploaded my perfect looking document into Kindle only to have its indentation shifting all over the place. While I was convinced the problem resided between Kindle Create and Kindle Online, their technical folks educated me on where the problem really resided, and that was within my Word document. I still wasn't completely convinced until I went to the start of a random paragraph and hit backspace until it merged with the end of the prior paragraph, and viola, there were spaces.
So, how do I prevent this going forward you may ask. Well, for one, stop using tab. Use the enter key instead. And to do this, set Word up so it will start a new line indented at a preset insert when the enter key is pressed. To do this you:
1) From the Home tab right click on the Normal option within the text labels (this is where it shows Heading1, Heading 2, Title and so on with what the type will look like above each one.
2) Select Modify from the list of options.
3) In the bottom left corner of the box that comes up, select Format.
4) From the list, select Paragraph.
5) From the box that comes up, and in the Indentation section, set the left and right numbers to 0.
6) Under the Special option to the right, select First Line.
7) To the right of that set the indent size under the By option. I use 0.2 which indents to the third character (I think about 5MM).
8) Hit okay to commit the changes, and okay again to close out the second box and you are ready to create you new masterpiece within Word without risk of those pesky spaces.