Perhaps all that is possible right away is to provide food, water and maybe nest boxes for birds. This, coupled with growing some annuals and perennials that provide food is a great way to get started and allows you to enjoy the sight of birds and butterflies while you are planning Phase 2. In the meantime you are creating a map of your property and considering the design of your garden. Garden design software can be very helpful at this stage, since many of these products can create snapshots of the garden at various intervals in the future. There may be no large trees, or any trees at all.
Trees take time.
However, you discover that there are a number of native shrubs acclimatized to your area that will provide cover and even food for birds and butterflies. Sadly, native plants, which are best adapted to local environments, are rarely used in landscaping. We have had a difficult time in our area finding a supplier for indigenous plants. The search is worthwhile. The native shrubs will offer cover and food to the birds in the short term.