The most powerful missionary message you can send is your own example of living a happy Latter-day Saint life. Remember that people do not join the Church only because of gospel principles they learn. They join because they feel something that begins to satisfy their spiritual needs. If you are sincere in your friendship with them, they will be able to feel the spirit of your testimony and happiness.
In addition to setting a good example, you can "be ready always to give an answer to every man that asketh you a reason of the hope that is in you" (1 Peter 3:15). You can pray for opportunities to tell others about the restored gospel. Then you can be alert, because many people yearn for the truth.