Being a very simple person and a newbie to AS, I'm using a very straightforward and VERY basic approach. I'm copying and using backgrounds from the Extras section of 'Tales Animator'. This used to be my main animation program.
(Yes, yes, I know it was designed for children and you used scripts (literally scripts) instead of frame-by-frame manipulation --- but don't forget my first 5 words above!)
http://www.dollysoft.com/extras/index.p ... rounds.pc0
I made a lot of the ones that are clearly drawn - using that ultra-sophisticated and
Sooooo complex program MSPaint. For my purposes this is proving perfectly adequate but wouldn't be too useful for someone who wanted more sophistication. However. for carrying out experiments, it's proving to be a very time-saving way of doing things.
Something else I've tried (again, purely as an experiment) is to load one of those images into Photoshop (but it could also be
any image intended for use as a background and any image-editing software), and to then use a blur filter. This can enhance the 3D effect when unblurred characters are in the foreground. Again - too simple and basic an approach for the more experienced users of AS, but then that's not me. (Yet)
One other small point about the readymade images available from the 'Tales Animator' website - there are also a number of foregrounds which can be used as - er - foreground layers once the blue areas are made transparent. For that I use the equally sophisticated and
Sooooo complex program Irfanview.
http://www.dollysoft.com/extras/index.p ... rounds.pc0
In the cases of both the imported backgrounds and forgeounds, I sometimes crop them outside AS, or I leave them as they are and just use Translation to select the area(s) that I want. Layer-scaling also works, of course, although the proportions of TA images aren't exactly the same as those of AS, so there is always a small part remaining outside the frame.
As you can probably guess, I tend to eschew over-complicated ways of doing things and look, instead, for the most direct, fastest, simple and least migraine-inducing.
One small afterthought. The developer of TA seems to have either gone around the world for an extended holiday or stopped the development of the program - so I can't guarantee how long the site will remain active. It's been OK for the last 6 months or so but ..... ???
Now I'll shut up and go back to sucking my thumb.