These "big things" can include going on overseas missions trips, taking part in complex church programs, or even leading some sort of ministry that touches the lives of hundreds. Any of these "big things" can be fine, but they are not necessary.
Anytime we treat another person with the love of Christ we are doing something significant for God.
You probably have a busy life. Almost all of us do. I work about sixty hours per week. It is difficult to find time to meet with other believers or reach out to the lost in my community. What, then, can I do? I can love anyone I come into contact with. Due to my work schedule I'm around my co-workers a lot. Instead of thinking of my work as something I only do to make a living, I can and should think of it as a primary location to lovingly serve others.
To quote a song that means something far different, love the one you're with. Whoever you meet in your daily activities, love them. This will, of course, mean different things in different circumstances. However, when we are kind to others and give service as is appropriate, God is pleased. I'm convinced that our Lord simply wants us to love the one we're with, regardless of situation.
Don't worry about trying to do "big things for God." If you will just love others by giving sacrificially of self, you will be doing exactly what you should. We can take comfort in the fact that God takes joy in our doing simple yet profound things for Him.