First, decide on what it is that you want to accomplish with your new landscape project. Do you want to be able to better utilize certain areas of the yard? Do you want to add outdoor entertainment areas? Improve the street view / entrance to your home?
Next, decide on your budget. Is the scope of the project in line with other homes in your neighborhood? There's an old rule in remodeling homes not to be the most expensive house on the block after everything is done. The same goes for your landscaping. You don't want to install a $45,000 landscape project in a home valued at $120,000.
Make sure the contractor understands your vision and will be able to implement it.
Include the contractor in the designing process so there will be a consistent implementation from conception through construction to finalization. Many landscape contractors have in-house design services.
The contractor should be properly licensed, bonded and insured. Many regions require special licenses to conduct earthwork, grading and plumbing operations. Liability and worker's compensation should also be covered.
Check references to make sure the contractor has experience on similar projects both in nature and size that you're considering.
Ask about experience with special products that may be used in the project. Is the contractor certified or trained by the supplier? Ask. Is the contractor a member of local and national trade associations?
What guarantees are included in the project? Many landscape contractors or nurseries will guarantee plant materials for up to 1 year. Hardscape installations should be for 1 year or more. Find out what is covered under the guarantee and make sure you have a written copy that should be stored with your property documents.