Show the change, not just the finished garden. A before and after slider is the most convincing thing a landscaper can put online.
Help people find work like theirs. Someone with a small courtyard doesn't want to scroll past acreage jobs, so simple filters make your gallery much more useful.
Be clear about what you do, whether it's design, full builds, ongoing maintenance or all three. That way you get the enquiries you actually want.
For most landscaping work the first step is a site visit, so make that the main button on every page.