Question
We have a large, aluminum-fenced backyard with a slight slope.  We have planted some trees.  What is the best way to handle all this space?  We find it a little overwhelming.

Answer
Like an artist confronted by a blank canvas, or a writer stumped by a white sheet of paper, it can be daunting.

Since I don抰 know anything about where you live or what your family enjoys doing, it is hard to lay down hard & fast design options for you.  

Here is a simple primer on landscape/garden design:

http://www.aperfectgarden.net/Landscape%20Design.htm

I would suggest you review the principles in the beginning of the link, above, then jump down to the section on 揝teps on Developing a Landscape Design? and really think about the six steps, listed:
1.  Plot Plan ?Show what is where, usually at a scale of some sort.
2.  Site Analysis ?How is this space laid out, in relation to sun exposure, access, utilities, trees/shade, areas that are not usable, easements, steep topography, etc?
3.  Needs & Desires ?What do YOU want to do in this space?  
4.  Activity Areas ?Where will these activities take place?
5.  Design these Activity Areas ?What will they include or exclude?
6.  The LAST thing to worry about is what kinds of plants to plant & where

Each of these items can easily take up several paragraphs of description. Take your time & think through each section - even tasks as simple as "WALK TO FRONT DOOR" - it is important for guests to be able to find it!  Many larger homes have secluded entries that are tough to find in a rambling estate.   

You design the overall space to fit your life and lifestyle, plain & simple.  Making it an attractive place to be in and enjoy is the 揳rtsy?part of it.

One standard design principle is to start immediately around the house and driveway, and move outwardly, adding areas for various uses (overlook area/decks/patios? Gardening zone (needs sunlight)? Sitting and having meals? Car repair? Crafts?)  and activities (walking trails, kiddie play area? swimming? pet/animal facilities, barns, pens? Raising Koi/Lamas/Quarter horses/bunnies/chickens? etc.)

Step 4 & 5 is where the real design takes place.  Step 5 is the budget-buster卆nd the most intensely personal part of this whole exercise.  

Again, think it through, as to what you and your family hope to enjoy in this wonderful oasis you call 揾ome?

I designed one large estate where the husband collected cars, and had a wheel-chair bound wife.  He had concrete trails throughout with sitting areas placed along these trails, so he could walk/wheel his wife around their estate and stop every so often to enjoy the view.  And, the garage area was HUGE! A 16-car complex with carriage house and entry pond (complete with pathways to enjoy it all with his wife).

Oh, If I didn抰 a budget, for most of us 搉ormal?folks, cost is THE limiting factor.  Not everybody can have a helicopter pad or world-class horse arena in their landscape design.

Good luck and happy dreaming!  -Marc