Hi Staci and Jewell! Thanks for joining in the chat!
First, I agree that for almost any kind of unimproved soil, "compost cures all ills". You can buy it my the bag, or make it in a pile from kitchen scraps and leaves, shredded paper or grass clippings. Coffee grounds are great. Unimproved soil is probably hungry for almost anything organic.
One thing that I haven't done as much of as I should is "cover crops". Clover, fall rye, or mixes of cover crop seeds will help suppress weeds, improve the soil, and add organic matter to it. You could sow those cover crops on spots where nothing else is growing. They are some of the easiest things to grow and will show you where your best spots are.
Then you can add the tops to a compost heap or use them as green mulch (sheet composting). The soil that their roots have penetrated and improved can then be shoveled up and moved to your flower beds, making THAT soil deeper and richer.
>> mostly shaded backyard
Sympathy! Keep your eyes open for patches of sun, and watch where they appear at different times of day. Maybe even trim a few low-hanging limbs if there is a partly sunny spot that you could make sunnier.
When you know what you most want to grow (cool season crops or summer crops) you can decide whether you care more about sun-in-spring, summer sun, or sun-in-fall. There might even be cases where afternoon sun is more desirable than morning sun (or vice-versa). .
Me, I just put my beds wherever I have ANY sun. Then I discovered things like "cold frames don't do well if no sun hits them until late afternoon!" But when I find something that DOES thrive in a certain spot, I plant it there again.
My suggestion would be to start with easy things, and see what doles best, where. Then stretch your wings.
Are you thinking mostly flowers, mostly crops, or a mix? I'm new enough to gardening that I still get a thrill any time "they didn't all die on me!"
>> sloped
If your soil is heavy clay like mine, "sloped" is an advantage. It means you have drainage. You might want to make your beds level so that rain and watering sink in instead of running downhill and taking your topsoil with it. One way is to keep the beds narrow and run horizontally "along" the contour instead of "up-and-down".
Also, if your soil is clay or drains very poorly, when making a bed or a raised bed, you might want to start "at the bottom" and level off the "floor" before you improve the soil above the "floor".
1. IF the original slope of your ground is
steep, set up some kind of wall along the DOWNhill edge of the bed. Stones, cinder blocks, a railroad tie, wooden boards, or concrete pavers stood on end. If your slope is not very steep, you only need "walls" if you build raised beds. But a "steep" yard might want beds that look more like terraces, or terraces with walkways between them.
2. Now break up the soil along the UPhill edge, and pull or shovel it over to the downhill edge, until the floor of the bed is mostly level. Ideally, it should slope downhill just enough that excess water will DRAIN downhill instead of pooling in your bed and drown your roots.