I'm proof that what you do isn't worthless. I have an amazing group of friends who were willing to share their faith with me, and they let me share mine in return, and here I am setting my baptism date.
Ya know what the one requirement is in all of this? Patience. Actually, I lied, there's a second one. Kindness.
Patience means that some people take years to start thinking maybe the LDS faith is for them. It took me at least three years, I think, if I'm doing my math right.
Kindness means that you never push people to believe as you do. It means that you ask questions about what they believe. It means that you accept that some people will never change their minds. It means that you be a friend to everyone, regardless of their religion. It means tolerance, and even more importantly, acceptance. If you come across as pushy and aloof, no one will listen to you. Yes, we believe that the Mormon faith is the one true Church on earth. No, we do not force others to accept this as fact.
Think of it this way.
I was originally Catholic. Now, if a Catholic came up to me to try to bring me back, would they be able to do it? Nope. By the same logic, if I walk up to the same Catholic to try to convert them to Mormonism, could I do it? Nope. Unless Heavenly Father prompts a change in their hearts, there's nothing I can do.
Kay, so now I'm contradicting myself, right? Only kinda. You should always be willing to share your faith with others. And don't feel like you're not making a difference. My friends made a huge difference in my life. But don't expect that your sharing your beliefs will always "work". D'you know what? Being pushy just makes people less likely to hear you.
We all just wanna understand each other a little better, right?