How to have a better relationship with my dad?

Well my dad isn't a bad father, but he is in prison currently and I don't know when he's coming out. He's been in and out of prison/jail my entire life, and I'm only 16. The longest time he has been out is about 3 years, then he went back, came out again for about 2 years, then went back again. He was even in prison when I was born doing 8 and a half years in prison. So all in all he has been in my life about 5 years the other 11 years of my life he was locked up. He just recently went back to prison, about 2 and a half years ago. He calls my mom a couple times a week and sometimes I will talk to him. We might go visit him like we use to when I was younger. I know we won't have the kind of relationship we would if he was out. But when I talk to him on the phone, I don't really feel comfortable talking to him or don't feel like I can ask him and talk about what I want to with him. How can I improve that?