I understand this situation as I was in it not long ago. Your interactions with those people and what they see of you will be your biggest message you can send. I also work nights and, although it is tough some times, there is always opportunities to serve either your church or just helping people out around you.
The best advice is stop trying to learn so hard, and instead, let God TEACH you. Pray for wisdom before you crack the Bible every time. Develop a true and genuine relationship with Him in your every day walk. Just open conversations and feel the great comfort of His love. The only way to grow closer and learn more, is to spend time with Him just like a friend on earth. The "basics" are essential and feeling confident in those is all you need to speak to someone. When you truly discover who you are in Christ, speaking about God is speaking about your Father. If I were to recommend some places for you, it would be Romans chapter 8, Galations 5. All of Paul's letters are exciting for me to read and I get something new out of them every time. The best way to witness to someone is to share with them your story, relate to them from your past or just let them lead the conversation. Don't be nervous of the rejection, let the Lord guide your words. If they reject the message you are telling them, they are not rejecting you, but Jesus.
Kind of scatterbrained tonight, but glad I found your post...needed to refresh my mind a little bit.
Have a good night!