Really not that complicated.... but.... you will need the Layer Mask Action to make life much easier. PSE9 has a Layer Mask (as does CS, of course). If your Elements is older, you'll really want a Layer Mask Action - Full information about installation and use are at
here on About.com, but you can Google for others.
If you've got the Layer Mask installed, here we go.....
1. You need some kind of theme for the montage - or at least something that links the different parts of it.
My choice of local landmarks and features is simple and perhaps an easy starter, but let your imaginations work a bit. Gather your pictures, perhaps in one folder but it doesn't matter as long as you can find them all again later. Don't worry too much about sizing of them - putting them in a montage is quite forgiving unless
you have to stretch an image so much that the pixels are obvious.
2. Create a new file - I decided to make my canvas enormous - in fact it started out with a canvas of 78" x 51", at 72dpi - you don't really need higher resolution because you can reduce your final image for printing and it will still manage above 220dpi even on the largest home printer. You should think of the final dimensions of the biggest print you can get and go for three or four times the maximum printed width you can achieve - my canvas is three times the width of my printer and keeping things to easier proportional measurements will make life a little simpler when reducing later.
3. Have a think about a colour scheme for your background, and whether you want some additional texturing. However, all this can be done at a later stage.
4. Open your first image thaat you want on the montage. Select All (Ctrl+A), Copy (Ctrl+C) and move the image onto the montage with the Move tool. You now have a layer on top of your background. Still with the Move tool, move it and resize to roughly the location and size you want.
5. While the Layer is selected in the Layer Palette (whether or not it still has the Move handles) double click on the Layer Mask Action. Click on the Mask itself (the box to the right of the layer). Make sure your Colour Palette (bottom of tool bar) is showing Black and White (just hit 'D'). Zoom in until the image of the new layer nearly fills the window.
6. Go to the Paintbrush Tool. Choose a soft-edged brush, at 50% opacity. Let's start with about 40pixels width on the brush. Check to make sure that the Mask of the Layer is highlighted (double border).
7. Work away with the brush 'spraying' the edges of the image with the black until the image is just down to its main subject. You will see the Mask becoming grey, then black, where you've 'sprayed' it and the image will lose any unnecessary surrounds. Generally, once you've got rid of any sharp edge to the rectangle that holds the image then you're nearly there and only have to concentrate on getting closer to the image. If you feel you have taken too much off the subject, change colour to White and 'spray it back in' - Black hides parts of the image, white replaces them.
8. Things to be careful of..... a brush that is too 'hard-edged' will leave too much of a boundary on the edge of the image. Too much opacity will eradicate parts but leave too sharp an edge. Too big a brush will start to remove parts of the image you want to keep.
9. OK, you should have a soft-edged subject somewhere on your canvas now. Move it wherever you want for now. No need to be too accurate - you'll want to shuffle things around later.
10. Carry on adding your images in the same way - if you find you have too many or maybe too few, you can reduce or enlarge any or all of them one at a time.
11. One quite useful tip is to try to find parts of images that can work well together - diagonal lines on one image can fit snugly against diagonal lines on an adjacent image - think "jigsaw". It's easy to end up with rows of images all laid out in a grid (some of mine are) so try to avoid this with the jigsaw effect and moving things around, adjusting sizes etc. Crowding the pictures together, rather than leaving big 'valleys' between them, seems to work better. (Nobody said this was a 5-minute job!).
12. You'll notice many layers building up as you keep adding new images. Resist the temptation to flatten them. They will almost always require later individual adjustments.
13. (No number 13)
14. Some images will have stronger tones and colours than others - avoid having some really overpowering images with the use of the opacity slider for each layer, toning down the strong images to fit and blend better.
15. There's nothing to stop you changing the colour of the background at any time, but easier to do that by making the background itself a layer. Same with any textures. (I prefer finding an image with the right textures rather than using the rather cheesy(?) PSE 'Texturiser'. I may be missing something about the Texturiser but if I'm adding a texture I want to use the tones and colours of it, or change them as I like.
Keep any texture as a layer on its own - you can colorise it or change blending modes to find an appropriate effect.
16. It's all Layers - you can add or remove as you like. If something doesn't seem right, try another image.
17. My montage was of a particular city - so I added the name of it (as another layer, of course). All standard PSE stuff - you might like to allow space for your title when you're doing the jigsaw.
18. If you need more space on your montage, just increase Canvas size and then stretch the background layer to cover it but beware of making it too big - be aware that a really huge canvas like this is a really huge file - I don't have a 'super-computer' but I do have lots of RAM. My montage, unreduced and as a PSD, weighs in at 297Mb
18. All this without scissors and glue! Have a good montage.