One of the problems of the area that jumps out at me is all the blank wall space on your neighbor's house. It's a primary view that a tree would take care of. On your own house facing the street is some of the same, so another tree is in order. Insofar as giving a sense of privacy while not enclosing, I would suggest a spaced series of small, multi-trunk trees -- like crape myrtle -- that insulate from view anyone who is a distance away on the street while it allows you to see what's close. If you spend some time developing a good trunk arrangement, you'll get more screening (like a visual filter) out of the trees as the trunks develop. To develop the privacy even more and get a sense of protection, place a bed of groundcover below the multi-trunk trees. It should a height that allow your view to easily continue above them. You'll be viewing below the tree canopy and in order to do that, it should start at about 9' or 10' off of the ground. (I pollard crapes to 10' every year.)

d keith, The idea of planting on a hill is both to prevent erosion, which is really important, and to look really nice. Full sun, zone 7, great for erosion, crape myrtle, buy more of them. They are wonderful, they have strong roots, you already have one there, and will provide a little bit of shade, which most plants will appreciate since you have sun all day. They will be on sale now, so buy more crape myrtles, they are anchors. Buy a chase tree, gorgeous blue flowers, no maintaince, drought tolerant, loves sun. Get at least one chaste tree. When you plant it, add some composted cow manure in the whole since you have clay, for the chaste tree. Evergreen magnolia is wonderful for a hill! Look for them at big box stores or nurseries now. Their roots spread out, and they grow great on hills. They are easy to care for, love sun and are evergreen. Get at least one of those, you will love the fragrant flowers in spring. The reason for the trees is important, they are the first line of defense against the pouring rain. It first hits the trees, they provide cover. Then you look for shrubs, a medium cover, like roses, which are wonderful and hardy, and also love the heat and sun. So buy some medium sized roses. You can use a soaker hose to water them. Also ornamental grasses are beautiful, and sort of medium size. Grasses need water though, so if you put out a soaker hose, include them in the path. The junipers are a wonderful suggestion also. there are ground cover junipers, you can plant them here and there, they are evergreen, which is good, they are ground covers, so they will also help the ground stay where it is. St. Johns Wart, sedum, ajunga, daylilies, little spirea shrubs, just a few suggestions as to some plants that you can plant around on the hill and will take fast. Good Luck to you.

If it were me, I would get a couple big, empty tree containers from somewhere and a good pair of loppers and just start at the back door, or any corner you chose, and start cutting that stuff down and cutting it up to make compost out of it. Put the tree container compost bins somewhere along the fence and start filling them up. Drag a bucket along while you work to pick up the inorganic debris/garbage you come across.. In fact, that is just what I did at my first house with a backyard that looked somewhat similar to yours. It is a real drag that there is no gate back there anywhere with a nice, big alleyway dumpster to access, though. Might look at a sat map of your area and see if there is anywhere, any way, any reason to put in such a gate in though... Once your weed cuttings have broken down a bit in your bins (maybe starting in 3 months or so), drop a couple handfuls in another bucket, add water, let the stuff stew for a couple weeks, take out a cupful, strain it, put it in a garden hose sprayer and use it for fertilizer on your cleared areas. It's called weed tea, and makes a good, cheap soil booster, useful at least until you get some real grass seed taking hold, and some real plants (desirable plants, that is) planted in there. Oh, final tip, pulling weeds is usually much easier after it rains....

Raymond, a regular Houzz contributor, Benjamin Vogt is a landscape designer in Nebraska. He specializes in native gardens and is incredibly talented and knowledgeable. If you border a pretty natural area, he would be invaluable in helping maximize the lots potential. Seek out some of his articles if you have a chance. Good luck!