What is some advice you have for a person aspiring to be a preacher?
First, study. You can't preach accurately what you don't know. "Be diligent to present yourself approved to God, a worker who does not need to be ashamed, rightly dividing the word of truth" (II Timothy 2:15). If you need some place to start, start with I Timothy, II Timothy and Titus. These are the books written to young preachers about their work. Then read Acts for examples of preachers spreading the Gospel and the Gospels to learn how the Master Teacher, our Lord, taught people.
Second, you can't preach well if you aren't an example of how Christians ought to live. "Let no one despise your youth, but be an example to the believers in word, in conduct, in love, in spirit, in faith, in purity" (I Timothy 4:12). The mark of a false teacher is the disconnect between what they claim and what they do (Matthew 7:15-20).
Third, work with a few older preachers for a while. Everyone has their own style and techniques. You'll have to develop your own, but it is good to work where you can ask someone how to handle hard situations and experience things you might never had thought about. "And sent Timothy, our brother and minister of God, and our fellow laborer in the gospel of Christ, to establish you and encourage you concerning your faith" (II Thessalonians 3:2, also Romans 16:21). "For this reason I have sent Timothy to you, who is my beloved and faithful son in the Lord, who will remind you of my ways in Christ, as I teach everywhere in every church" (I Corinthians 4:17). An older preacher can also help you in your personal studies
Finally, one doesn't have to be an "hired" preacher to preach. Start doing the work where you are. Get "on the job" experience. As an example, I preached for twenty years before I ever received financial support for preaching, so I'm not suggesting anything I haven't done myself. That does mean you have to have a way to support yourself while you are preaching. And such experience becomes important later. Most preachers, myself included, have to work two jobs from time to time to make ends meet. If you aren't in a position where you can support yourself, you may find yourself threatened to conform to some teaching or face losing support. Few things irritate me more than brethren thinking they can get their way by using funds as a club. It has always been useful to me to be able to say, "I don't need your money. Now, let's get back to what the Bible says about the matter."