I've learned:
1. If your theology isn't practical and applicable to your Christian walk, it is either bad theology or not worth spending time on. Probably the former. To borrow a phrase from Flip Benham, you should be "making theology into biography."
2. All valid and correct doctrine is practical and applicable to one's Christian walk. The study of so-called "theology" is nothing more than simple Bible study, and is therefore relevant to every Christian, everywhere, from the genius seminary professor with four PhD's to the Down's Syndrome man who has barely enough mental acuity and maturity to reach a minimum "age of accountability" and have a genuine, sincere faith in, and relationship with, Jesus Christ. Because every Christian's walk with Christ involves "How do I pray?" and "How do I relate to other people?" and "How can I serve God?" and "What is the gospel, the good news of salvation?" And all of that is "theology," ie. Bible study. I have met pre-teen children who have a better grasp of biblical doctrine than the average Christian adult, I kid you not.
3. All theology is intertwined and related. Nothing stands alone; everything is connected. This is why I lean heavily toward a perspective of systematic theology, although a "biblical theology" perspective is often valuable input in many issues. All doctrine is related to numerous other areas of doctrine, sometimes even to areas that many not be readily obvious, at first.