First, reduce the size of images if you can. If you use any images then scale them down on the canvas in Construct then you want to actually resize the source image.
Second, take a look at the animations and remove any unnecessary frames. If you are new to animation you may need to do some experimenting with what frames to remove, but the chances are high that you have too many if you are just starting out.
Third, reuse any image you can as much as possible. I like to consider this as much of a skill as animation, it may take some experimenting with what should be reused and what shouldn't, try your best to look at a scene as a whole. To learn this study games you respect by getting a screenshot and scanning the image with your eyes, you'll notice that there are never as many unique objects as you think.
Forth, Whenever possible utilize tile maps and tiled backgrounds. Large background images will really add up fast.
I wish you luck, these were the things I needed to work on when starting out.