The first semester is always the hardest, for most people. I know it was for me, and for most of my roommates as well. We were all just getting adjusted to living the "college life". We were away from home for the first time, with no parents and really no supervision at all. We had so much free time in between and after classes and we would spend most of that time doing just having fun and doing absolutely nothing with each other. As one would expect, during this time grades were not a major concern. We were invincible, and therefore, pretty much everything else was higher on the priority list than grades were. All fun and no play does, in fact, have its consequences, as evidenced by this way of thinking and acting leading to the exact result you would think it would lead to. This is probably evidenced in many more freshmen GPA than just mine.
There is no reason to worry, though. Just because your first semester goes by the wayside doesn't mean that your entire college career is down the drain. The best thing to do is regroup. Think about the classes you took that first semester when you didn't do so well. If you didn't enjoy the material, that is probably one of the contributing reasons as to why you didn't perform as well as you hoped, and you should try and stay away from classes like that in the future. If you did enjoy the classes and you want to keep pursuing similar ones, focusing on the work and blocking out all outside distractions is essentially the best way to raise your GPA back to where you want it to be.
The first semester should be used mainly to learn. You are getting your feet under you, learning the lay of the land, and experiencing what you need to do in order to achieve. You need to make sure this is the place for you and that you want to be here for the next few years. Once you realize where you want to be and what you have to do to succeed, everything else will follow suit.