..Planning
..Designing
..Choosing your plants
..Putting trees in your Design

Planning

The first step to landscaping is getting your plans on paper. The easiest way to do this is to measure the area to be landscaped, and then transfer these measurements onto graph paper where each grid represents a certain distance. Be sure to include distances from existing plantings (trees, shrubs, etc.) to permanent structures, such as your house. If you are landscaping your front yard, take the measurements of your house, then your yard. Place existing trees, shrubs, etc. in your drawing the correct distance from each other and from your house. Now you are ready to design.

Designing:

Your design should have several goals in mind:
low maintenance- mowing should be easy and minimal, with a mowing strip around beds ; beds should be easily accessible for weeding and planting, using landscape fabric in perennial beds; ground covers should be used in place of sod, where possible; low maintenance plants should be used for foundation plantings (plants placed along the front of the house).
stay within your budget- decide on how much money you can afford to spend. Landscaping doesn't have to be done all at one time. You can design a plan for the entire area, and then do one section at a time. Determine the cost of materials (soil amendments, equipment rental, landscaping fabric, edging, plant material, etc.) for each part of the entire job, and then plan to finish a section at a time. It is better to work in sections than to remove sod from the entire planting area only to find that you can't afford to get all the plants you'll need until later. Also, your yard will look much better if you complete a section from start to finish without delays in between
create a flow- plantings should flow from one area to another. You don't want it to look like you just dropped a flower bed into the middle of the yard. You can enhance the look by using curves instead of straight lines. This also will make mowing around plantings easier. Curved plantings can soften the area around mailboxes and utilities.
create a theme- not all landscapes have to have a theme, but you can create a theme based on the kinds of plants you will be using. For instance, if tropical looking plants do well in your area, and you like the look, you might want to go for a "tropical" theme in your landscape. If you would rather use old fashioned plants, you can go for a "cottage garden" theme. If you like a well-manicured look, you can use different types of needled and broadleaf evergreens for an "estate" theme.

Choosing your plants:

You should choose your plants according to the theme you are using (if any), what kinds of plants you like, what plants do well in your area, and the growing conditions (amount of light, water, etc.). Also consider the growing habits of each plant. The size of a mature plant should determine whether or not you can use it in a particular area. You don't want to place a plant under a window if it is going to grow tall enough to obscure the view from the window.
Choose plants for the area that they will occupy- shade loving plants for shady areas and sun loving plants for sunny areas. Plants that may require more watering than others should be placed closer to a water source so they can be watered without much trouble. Drought tolerant plants can be used in areas where watering is difficult. Consider planting perennials with broad leaf or needled evergreens- when the perennials go dormant during the winter, the evergreens will remain green so the beds won't look bare. Consider planting annuals around broad leaf evergreen shrubs that bloom in early spring. When the shrubs have stopped blooming, you can plant the annuals to add color to the bed. Do not use landscape fabric where you plan to plant annuals. Instead, use mulch.
Plant bulbs in a bed with a low groundcover. The flowers will push their way up through the groundcover to bloom.
Use mass plantings of one kind of flowering shrub or flower for a striking effect. A few flowers here or there is fine, but a mass planting of one kind of flower is very eye-catching. eg. I once saw an entire front yard landscaped in low growing azaleas and tall trees. When the azaleas were in bloom, you couldn't imagine anything more beautiful!
Consider how the plants will look when they're in bloom, and when they are not in bloom! During the summer, they may look great, but during the winter, if they lose their leaves or die back to the ground, you should have something else planted there that will pick up the interest. Avoid planting a border using only one kind of plant if that plant looks good in only one season. A border of roses is gorgeous when it is in bloom, but in the winter, it is reduced to a border full of bare, woody canes- not very pretty.
Plants bloom at different times during the growing season. Try to incorporate perennials and shrubs with different blooming times together so when one has finished blooming, another is beginning to bloom.
Plan to place taller plants behind shorter plants and give them room to grow to their mature height.

Putting trees in your Design:

A tree is a wondrous thing. It can really add beauty and character to a landscape, but remember this- it will produce shade. How much shade it produces depends on what kind of tree it is, but you can be sure that you will get some shade from it. Make sure that you take this into consideration when you draw your plan. You don't want to plan for an oak tree with a sun loving flower bed under it, because it just won't happen. However, a Japanese Maple or a Crape Myrtle would probably work out just fine in that situation. When you plan for a new tree in your landscape, consider how it will look 5 and 10 years down the road. Then, your plan will be much more realistic and reasonable.

gutters: do not place deciduous trees (those that drop their leaves in the winter) next to the house.

septic lines: do not place trees with invasive roots, eg. maples, near septic systems.

decks, open porches, walkways, driveways: do not plant fruit producing trees near these areas.

driveways: do not plant trees or shrubs too close to a driveway, and do not plant them where they might obscure your view of the road at the end of the driveway.

swimming pools: do not plant deciduous, fruit producing, or cone producing trees near a pool.

power lines, phone lines, utility lines: consider the potential height of your tree before you plant it underneath power, phone lines, or other utility lines.

underground cables: be aware of the location of underground cables, pipes, and gas lines before you dig.

- Removing Sod:

Chances are, you will probably want to remove some grass and replace it with other plant material. Groundcovers are a great substitute, especially around foundations where mowing is difficult. If you are working in sections, this doesn't have to be a difficult task. Just start by cutting a small square into the grass using a spade. Push the spade straight down into the grass. After you've carved out the square, push the spade under the square (push the spade with your foot), and lift the grass up by pushing down on the spade handle. This will tear the grass from its roots. Instead of lifting the grass with the spade and throwing it aside (this can cause damage to your back or elbows), lay the spade aside and lift the square of sod with your hands. Shake the dirt off of the grass roots back onto the ground where you removed the sod. Place the grass in a wheelbarrow or some other receptacle to be discarded or composted later. Keep removing the sod in this way, following the curved outline of the area, until the entire area is cleared.
If you have a large area of sod to remove, you will probably want to rent a machine that will do the job quickly and easily for you.

- Preparing the Soil:

All planting areas should have well-drained soil. This means that if you have heavy soil, you will have to add soil amendments such as peat moss, leaf mould, coarse sand, compost, or rotted manure. It doesn't matter how much of each you use or which ones you use, but you should test the soil for drainage afterwards by watering it well and waiting to see if the water drains off readily or if it stands there for a long time after. If the water takes a while to soak into the soil, you will need to add more of the amendments before planting. Note: If you are making "raised beds", the drainage is not as big a factor as it is in ground level planting. If you have sandy soil, you will need to add amendments so the soil does not dry out too quickly. The above mentioned amendments, except the coarse sand, will work well in sandy soil.
If you are planning on installing an irrigation system or sprinkler system, now is the time to do it- after preparing the soil.

- Planting:

Before you plant anything, you should place the plants in the exact spot that they are to be planted. Make sure you are happy with the placement and look of the plants. Imagine them in a few years when they have grown. They should have enough growing space so they aren't crowded. If you are using landscape fabric, put it down before you set the plants in their selected locations. When you are satisfied with your placement of the plants, dig the planting holes. The holes can be dug with post hole diggers or with a shovel. Dig the hole wider than the plant, but only as deep as the root ball. The top of the root ball should be slightly higher than ground level when planted.

Information provided by: 
http://www.geocities.com/imadee/landscaping.html