Great advice, Ausette! I love the moviemaker cheat, there's so many options! I used it to create the 4x4 picture:
As you can see, I placed some well-known townies in some of the most iconic places in their towns. You may notice that on the top-left and top-right pictures (Agnes & Chris and Hunter Cottoneye) the Sims don't look like they're standing on the ground. Well, that's because they're not! Using testingcheatsenabled true, I used the raised terrain tool to create a little platform and teleported the Sims up there. There may be an easier way of achieving this but I thought it was a good idea
Sometimes a little bit of enhancement on a screenshot can make it look better. Even just a border can make an image more noticeable! These are two examples of mine from two contests (which I actually won):
I wanted to give my image a vintage look, as the Sim I was entering is supposed to be a classic film star. I achieved this using a website called Picmonkey (I believe it was in the borders section). The majority of tools on there are free and you don't have to sign up. I did also use Photoshop Elements, which is basically a stripped down version of Photoshop, so that her lips remained red while the rest of the image is black and white.
This one was done entirely with Picmonkey. To get the American flag, I saved and image and then used the 'textures' function in Picmonkey. There are a few already on there but you can upload your own, which is what I did. It's like putting another image over the original that is slightly transparent. Then I just added some text and a coloured border.
It's a great way for people to notice your entry, though it's important you don't go too overboard. Your entry still has to be clearly visible so that people know what they are downloading and voting for.
For actually taking screenshots, the Tab key is your best friend! You can get much closer than you'd normally be able to, which is especially good for taking images of toddlers or face close-ups. You can also try out interesting angles using Tab.
It can be frustrating when you're trying to take an image and one of the Sims is in the wrong place or facing the wrong direction. You can fiddle around with it, making them walk over there and then back again, but I prefer to just pick them up and move them around! Using the 'moveobjects on' cheat ('testingcheatsenabled true' must be enabled first'), you can just pick your Sims up and rotate them. Press the 'Alt' key to be more accurate.
Try to catch your Sim doing interesting things or when they have unusual expressions. Sims themselves have cool little interactions that can show off their personality. For example, the Irresistable trait has this interaction:
It can add a little more depth to your Sim's character.