My friends is having trouble facing her crush, what should she do?

Smile and occasionally look at them from across the room, then look away. Repeat until they smile back or approach you. If the smile seems a bit full on, try glancing at them, then look away for a split second. If they are interested they will most likely still be looking at you. If so, you could try a smile or if you're daring approach them.
Go up and introduce yourself to them. Guys/girls normally will turn on to you if you act friendly and flirt at a minimum, not if you full out lunge at them. That may freak them out. Be confident, not cocky!
If you are not so sure that they like you, ask them to do something outside of school possibly bring them to a park or with your friend and possibly his/hers as well. Then if things are going well ask if they want to go for a walk with you or something. Just you and them; nobody else.
If you feel that you're okay with it, tell them how you feel. Make sure they like you too; if not, things could get awkward.
Do your research about them, learn their favorite sport, hobby, etc. People are more attracted to those who are smart and those who take an interest in them.
Go over to them and start a conversation, they will respect you for it.
Make sure to have gum/mints candy. No one likes smelly breath.
Ask them out! They are usually hoping for you to do it (if you're a guy). Girls on the other hand might really want you, but they are too scared to ask you.
If they reject you, you can always have a clever come back! Like if you go up to them and ask,"Do you like me?" and they say,"Yes, as a friend." then you could say back,"Good. Me too. I was just asking because I thought you didn't like me as a friend." and so on so forth.
Make sure he/she is single! You never want to do anything with a guy who is already taken! You know he won't tell you!
Maybe if things are going well and you and the boy/girl have been talking in school for awhile, you can get their number!

tips:
Sometimes, it's a bad idea to tell all your friends you like him/her. The best of friends can go ahead and tell him/her.
Try new looks, a new haircut can do wonders.
A friendly smile is your best weapon.
Try to make them laugh; humor is the best aphrodisiac.
DO NOT insult their friends or anyone around them, petty malice is not attractive.
Don't hang all over them, they will think it is weird.
If you already know them and are flirting with them in the way of taking their stuff, if they ask for it back and seem annoyed give it back.
Do not stalk them. (aka: have pics of them, follow them, ext.)
warnings:
Don't change completely for them! A new look is one thing, but don't lose your entire personality in order to get with one person.
They may not be interested; this is only a guide, not a certified way of getting a boyfriend
Don't tell your friends unless you can really trust them. No one wants rumors to start or your crush to find out.
Don't be a dork and just stare. Be social and talk with them