Fixing figures to page locations is a bad idea when there are lots of them to put in because adding content above them will likely make any subsequent figures shift and overlap. This is kind of because they are anchored to a paragraph and a page location. Rather, anchoring them to a paragraph and allowing them to float with the text will work much better in the long run.
The best way, is to use frames although the necessity is going away with newer versions of word. Originally, frames ensured that the content within them appeared on the same layer as the content outside where text boxes floated on another layer. This makes cross-referencing impossible because the layers don't play nice. I'm not sure this is the case anymore though. In new versions of word you have to add the "Format Frame" button to the quick bar because it's not available by default.
Now, don't make frames and put figures into them. Do it the other way around. Put the figure into the document. Right click and insert caption. Then highlight the caption and the figure and click the format frame button. It will make a frame the correct height and the width of the page. Position the figure within the frame (i.e. center it) and you're done. The frame will be anchored to the next paragraph and will float nicely!