The main difference between boys and girls is that boys like doing things - driving cars, playing football, throwing stuff, eating, farting - and girls like feeling things, such as love, friendship, happiness and excitement.
Boys are very physical; girls are very emotional. This is a gross generalisation, but it helps to remember that when you ask a boy "How are you feeling?" he will probably answer "Hungry" or "Cold" and not "Deliriously happy because I am with you". To begin with, this can be disappointing, but it can't be helped, since expressing emotion comes as naturally to a boy as ballet does to an elephant.
If you are friends with a boy, bear in mind the following: boys worry a great deal about what other boys think of them. Therefore, even if a boy really likes you, he will be weird about showing this in front of other boys.
If he's very immature, he may ignore you completely when he's with his friends. This means he's probably too much of a baby to bother with, although you may wish to give him a second chance if he apologises and promises never to do it again. If he's actively rude to you in front of his mates, forget about him. He is not just immature, he is an idiot.
Boys are often spoilt by their mothers, so they have a tendency to think girls should do all the boring things in life, such as cleaning, cooking and ironing their T-shirts, while they do all the exciting things: jet-skiing, playing in rock bands, being spies. Don't indulge this belief; the sooner they get re-educated the better.
Boys don't always say what they mean and often don't mean what they say. Communication is not their strong point. They're not terribly sensitive to other people's moods either, so if you are upset about something, you will have to spell it out to a boy. It's unlikely he'll work it out for himself, no matter how much sulking or moody hints you drop. Just tell him what's bothering you and he'll probably be genuinely surprised and sorry he's upset you.
Although boys go to great pains to show the world a confident front, underneath they are just as insecure as the rest of us. Sometimes, when it's obvious they are feeling sad (you will know this through your superior powers of intuition), a bit of encouragement or a compliment can help them feel better.
One of the nicest things you can say to a boy is that he's good at something, eg skateboarding, running, building a tree house or solving quadratic equations. Remember these few basic rules and boys can be among the best friends you'll ever have. They'll carry your books for you, too.