These adjustments can be best controlled by using Rectangles. Rectangles can lock adjacent items in place so when they expand they don't push the other one down.
If it is images in particular causing you problems you may find your image is set to Original Size? This means it can expand and push down other items in the report. You can also change the image size property to fit-to-size or something similar (something that wont cause the cell to grow), however if this isn't appropriate you should be able to fix your problem with Rectangles.
Hope this helps.