What is the best way to start a Landscape Design Process , and what are the most important Determinants ?

I start a Landscape Design with the concept

There are ten important things to consider: Understand your site for plant selection and activity location Remember the user by considering what you want and need Use a form and/or style theme to help determine shapes and organize spaces Create and link spaces by designating activity areas and linking with elements Consider the function of plants for both the environment and the user Structure the plantings by using massing and layering techniques Highlight important points such as transition areas and focal points Pay attention to detail in the materials, the colors, and the surface textures Take time into account for the growth and maintenance of plants Protect your resources by using sustainable design practices

Thank you for your invitation.
Based on a personal experience, the very first thing you have to do after you meet the client and know his budget, is to make sure of the landscaping stuff that's available in the market, so your design and details can be implemented later if approved without any compelling modifications.
Then start your landscape design by:
1- Make your Design Analysis, through: A - Site visits.
This's a must, so the designer gets familiar with the location to know: a- Kind of soil: if it's clayey or sandy...
etc, to know later what kind of plants are to be used.
b- The Slope: to know if the location is flat or has some slopes,this decides later the zoning plan or areas' locations c- Land marks: many famous projects were based on land marks concepts, so if you have, for example, an old tree, a good designer should know how to make it the beating heart of his design.
d- Views and North: this is your guide line for some orientations.
A site visit should be memorized through taking pictures, panoramic pic.
is preferable, this's Zoning and detailing stages.
B- Getting essential plans and drawings: General site plan " with existing roads and services, existing buildings, if any", Topography plan or Contour drawing " that shows the benchmark and levels of your land".
Land profiles are also a good plus.

2- Now you can determine your Zoning Plan that shows: main entrances, main accesses, stairs, main areas: greenery and tiled areas, water features " if wanted" .
And Axis to main building..
so on
3- Next step is a designed site plan, based on zoning plan.
Site plan should reflect your general concept, your theme, and your design elements " spaces, shapes, masses, colors, balance, harmony...
etc".
Also shows types of plants to be used.

4- Light Details: through Sketches or 3d shots that show general main ideas in your design to help your client better understand your concept.
Style of your design, finishing, and materials are mentioned in general.

5- After approval, you have the final details: shots, plans, elevations, sections...
with specified dimensions and finishing materials.

Mainlly collecting the available information & visit Site, Then listinning well to Client, Put a Concept & Starting to draw this Concept Details.

The best way to start the design process is to determine the design elements witch include paths, trees, buildings, setting areas etc..
then decide on design style that you are using, once you are done start with the planning:
1- first lay down the main access point, buildings the existing and the ones you are creating
2- lay down paths, walkways, driveways and the access path for buildings
3- create the green spaces, plants beds for the paths, shading treas and wind barrier when you are done you review the design to develop and adjust as needed

 first to learn with in a acceptable way then building up experiences then working with clients who admires quality work

we should determine usage of each part to determine amount of lighting and after that we should select suitable light for every spaces.

Access (roads and infrastructure), water (availability, quantities, limitations/restrictions) and desired uses (only vieweing, food garden, children's park, etc). 

The first step is to do analysis of the space that is going to be landscalpe, interm of location, size, access road, adjoney properties toghter with the Client briefs, also choice of landscalping element must be consider.
the major determinant of landscalping is the function that is going to perform, either for security purpose or aesthetics porpose.

The question is quite wide. However, I think it is "Passion."  If you like what you do, you could do the great work.  About other issues, you can learn and read from institution, books or magazines.