1. Show them respect: most siblings fight a lot. If you want your siblings to be your friends, you have to show them the same kind of respect you show your friends. You would not take something from your friends without asking, so show your siblings the same respect. You would not try to embarrass your friends in front of a guy or girl they like, so do not do that to your siblings. You would not do a lot of things to your friends that you probably do regularly to your siblings. So, to make your siblings your friends, you have to treat them that way. It can be difficult to do this at first, especially if they do not give you the same respect. However, give it a little time, and before you know it, you will be friends. If you are older, and no longer living together, be tactful when you talk to them, often the rude comments, and thoughtless actions are what cause your friendships to suffer in the first place.
2. Hang out with them: you spend time with your friends doing fun things. You probably go to movies, have sleepovers, go shopping, to the beach, park, or whatever it is you enjoy doing. If you want your sibling to be your friend, do those things with them. You can invite them to come along with you when you go with your friends, or you can make plans just with them. Just make sure you spend time with each other away from the other members of the family, and beyond the family activities and responsibilities. If you no longer live in the same house, get together once a week for lunch. Shop with each other, or offer to pick things up at the grocery store for one another, that way you have an excuse to see each other.
3. Call them: You call your friends about nothing, so do the same with your siblings. Call them up, tell them about your day, ask about theirs, and just chit chat. You do not need a reason, just call for fun. That is a great way to become friends with your siblings.
4. Remember their important stuff: if you are their brother or sister and you do not remember their birthday, or other special events in their life, it is going to be harder for them to swallow than if their friends forget. However, their friends probably don't forget, and you shouldn't either. When you are a friend you care because you want to. So, show you care, and remember those events. Surprise them with a gift, or a card, or a phone call. Make a big deal out of it. Remind everyone else, and celebrate them. When someone makes you feel good about yourself, it is easy to be their friend.
5. Share secrets: have you ever told your friend something you did not tell anyone else? What does that do? It bonds the two of you. When you open up to someone and show them a side of you no one else knows, or an insecurity you have, or whatever it may be, it makes you closer. Do not burden them with your troubles, but include them in your secrets and you will be better friends.

Having your siblings as your friends is important because you are stuck with them for life. So, make them your friends today.