Place the Large Plants First
This may sound obvious but it's easy to get caught up with the pretty plants when wandering around the garden centre. Instead, start with thinking about where a tree (or trees) could go first. When designing a garden, trees are an important structural element so we make decisions about where to place these very early on in the design process.
Bear in mind overhead cables and avoid planting too near the house. Trees are a fantastic plant for any garden; they offer a home and food for wildlife and will make the garden more interesting overall.
There are plenty of smaller trees out there if space is limited too. The tree in the image is an Acer cappadocicum 'Aureum' and would be well suited to a small garden. They are slow growing and easy to maintain.
For larger gardens, consider having a few trees. Trees are wonderful for creating interest through height. Additionally, they offer a retreat and food for wildlife.