You know that you’re saved because salvation begins to appear in your life. You desire new and different things. The law of God that you regarded as an enemy and an irritation becomes a friend, and you want to keep it. You want to please Christ rather than let Him down. All of these are very simple things. You begin to love the people who love the Lord Jesus.
These are the kinds of things that 1 John speaks about. A good exercise would be to go to 1 John, which speaks about our relationship to Christ, our new relationship to sin (we no longer love it, but instead hate it), and our new relationship to God’s people. We begin to love God’s people and to want to be with them.