Always be prepared to give a defense to anyone who asks you for a reason for the hope that is in you. This paraphrase of 1 Peter 3:15 is commonly cited as a basis for apologetics. After all, you are giving a defense and it is about the faith. That is basically the definition of apologetics. Here I want to highlight a different aspect of the verse.
This is a defense of the faith. It is giving a reason for the hope that is in you. In order to do that, we need to know what the faith is, what our hope is. When Polycarp was being burned alive for not offering incense to the emperor, he would not have set the same example if his reason for refusing was that Jesus thought incense was smelly. Instead, his martyrdom was grounded in the fact that Jesus is Lord of all and that we should worship no other so-called god or lord. This is why he asks rhetorically, “How can I blaspheme my King and my Savior?”
So if you are interested in apologetics, you need to know theology. This is part and parcel of apologetics. Do you know theology well? The point is not to get bogged down in all of the particulars and different traditions. Do you have a good grasp of the broad contours of theology?
After all, theology is important in order to know what needs to be defended and what does not. Take the doctrine of the Trinity as an example. If someone thought this meant that we believe in three gods (the heresy of tritheism), then Christians would have to defend polytheism in their apologetics. On the other hand, if they thought the Trinity meant that the Father transformed into the Son who transformed into the Spirit (the heresy of modalism), then that view would need to be defended.
Unless one thinks this example means everyone already know the broad contours, let me provide an example that is more complicated. In “Understanding Omnipotence,” Pearce and Pruss analyze omnipotence in terms of perfect freedom of will and perfect efficacy of will. Does this analysis create a problem for the Christian due to God’s triunity? As Pruss writes in “A Gödelian Ontological Argument Improved Even More,” “But there cannot be two beings with perfect freedom and an efficacious will. For if they are perfectly free, they will be able to will incompatible propositions to be true, and then one of their wills shall have to fail to be efficacious.” So does this analysis of omnipotence combine with God’s triunity to prove that Christians have a contradiction on their hands?
This would be true according to how the Trinity is often thought about. Under this view, each person of the Trinity has a distinct will. Thus, there are three wills in the Triune God. Minimally, one sees this in extreme forms of social Trinitarianism. So for many laypeople and even some philosophers and theologians, there is a problem here. However, the historic faith has taught that the will is according to the essence or nature, so the Triune God only has one will. As Pruss notes immediately after, “This argument assumes that we are individuating beings in such a way that distinct beings with will have their own will. If God is a Trinity, the persons of the Trinity do not have distinct wills, and hence will not count as distinct beings in our sense.” 
Those who are aware of Christian theology do not need to twist themselves in philosophical knots in order to defend the Christian faith. Instead, a solution is immediately at hand. So if you want to do apologetics, you need to learn theology. You should be growing in your knowledge of the Bible and theology continually, so this is only an added emphasis. If you are pursuing apologetics without learning more about God’s word by understanding the Bible and theology, then you have made an idol. Where your treasure is, there is your heart.
So take heed and repent. Life is more than winning arguments or learning syllogisms. God promises us nothing less than fuller communion with Him. No theology, no apologetics.
I suggest the following short books:
(1) For theology, see Christian Dogmatics (eds. Allen and Swain). This comes from a more Reformed perspective, but it is short and solid.
(2) For an overview of the biblical storyline and major themes, see From Eden to the New Jerusalem (Alexander).
Do not write off reading these books. If you read at an average pace, you can read both books over the course of a month by reading for thirty minutes per day. You have the time. Trust me. If you do not believe me, look at either iPhone’s new Screen Time or download the app Moment.