Plant a Native Tree or at least one that is recommended for the area. Follow these links for more information about how to find a high quality tree; which native trees are recommended; and how and when to plant.
If you want more detailed information on planting, take a look at Cleveland-Tree-Plan-Appendix-A-Tree-Selection-Guide.pdf (clevelandtrees.org) and a Native Tree of Ohio complete list.
Planting native bushes and perennials is great too. Here is a helpful list of shrubs and perennials and a rolling list of “native plants of the year,” with colorful photos.
NOTE that the Cuyahoga Soil and Water Conservation District sells a variety of native plant seed packets, plants, and native trees, including conifers and broadleaf tree species. Lean more here. Most of this happens in the spring.
Do not let your oaks get diseased with “oak wilt”! You can protect your wilts by not pruning or cutting them during spring, summer, or early fall; prune and cut branches only after the first frost (usually in November) and before the first thaw (e.g., early March). Oak wilt is highly contagious and once it strikes it can kill many mature oaks and cost thousands of dollars in tree removal costs alone (not to mention the lost benefits). There are some chemical treatments for oak wilt, but they are not always successful and are generally very expensive.
More general pruning tips and additional helpful pruning tips here
Keeping trees healthy against insects, age, and other threats
WHEN IN DOUBT, GET HELP FROM A PRO
ALWAYS get help from an ISA Certified Arborist. Do not trust the fly-by-night “tree” experts who can leave tree diseases or cut at the wrong time! You will lose a lot more money than you save. To find a certified arborist or check their credentials go to Find an Arborist (treesaregood.org).