Relationships can affect your whole year. It is never too late to start or fix a relationship, but you should definitely do it soon. Like, right now. I was extremely socially awkward and I "refused" to establish good relationships with local people during my exchange year, and I know it was not the best. So be friendly and nice to people.
The key for a good, healthy, and even close relationship is communication. Talk to people, explain yourself, and ask questions. It never hurts to ask what you don’t know, and you probably don’t know a lot of things. But if you keep silent then you won’t learn anything eventually. So ask. Besides, there are some things you want to keep in mind.
First, explain your lifestyle with your roommate(s)/host family and learn theirs. You are going to live together for at least a year and you want to know how to live harmonically together. Ask them about what they expect from you and your duties in the living place. Share your feeling with them. Going over these “rules” will help you avoid “inappropriate” deeds and do the “appropriate” ones. I didn’t really do this, and we misunderstood each other for nearly a year. Believe me, you don’t want that to happen.
Second, as everyone may already tell you, say “thank you” and “sorry” all the time. It may not be a habit in your culture, but it is necessary to show appreciation in this country. If you are not used to it, it’s okay. Tell people you are learning and you are getting there, and sometimes you may forget. As long as people know you are grateful or sorry, it’s good. Of course there are people who don’t care or just know, and people who will have no idea if you don’t tell them. I’d say rather than not saying anything at all. I forgot to say thank to on of my friend and she thought I took what she did for granted.
Third, small talk is typical in US culture. Many people may not be familiar with it, but it is there. One of my suggestion is come up with some fixed small-talk questions you can talk about with someone, like talking about weather, study, etc. Likewise, you will soon realize the the teacher-student relationship here can be quite informal and close, so if you want to be friend with your teachers and if you are kinda socially awkward like me, come up with some questions to open a conversation. You’ll get used to it.
Finally, there are things I had learned when I came here. Tip is necessary and even mandatory, and often it’s 20% of the total bill. Asking for a ride is not hard at all. People are often very friendly and will take you. Sometimes they will offer to bring you. Car is not a problem, but gas is. Offer to pay gas. It’s serious. It shows politeness and appreciation. No matter if the driver accepts or declines, do offer to pay. Prepare $20-$40 for a two-hour drive.