The easiest thing you can do to get parents to help you and agree with you is to take reponsibility and step up rather than suck up. So, saying something like "If you buy me these jeans now, I'll do the dishes all next week to pay it off" sounds better than "Pleaseeeeeeeee, I neeeeed these jeans! Puh-leeeze!!!!" If they still say no, leave the door open by asking if you could *insert thing/activity here* next time, or in the future.

2. Friends.

Oops! You've said the wrong thing or done a dirty deed and now your bosom buddy won't talk to you. Taking steps to recovery and friendship isn't easy, but you can do it. First thing- when you apologize, don't lay any blame. Don't say "I know I said mean things about Bob, but you totally overreacted." Likeliness is, she had a reason to overreact and that should be discussed instead. Next, don't avoid talking about the subject, it needs to be out in the open, no matter how many awkward conversations it takes. Last, tell her/him why you need them. Make sure they know you care.

3. Teachers.

Here comes your interim, and...wow, that is one grade you weren't expecting. Well, don't worry, there's probably a way to improve it. Next class, ask the teacher if she has any extra credit work. If not, then ask if there's any way to raise your grade, or if she'll give an exception if you do extra work. The key is that you indicate that you will be willing to work for the grade, and that you're determined to do well. Admit that you've been behind or slacking off or don't understand, instead of refusing that there's a problem. The teacher will probably sympathize if they realize you will do your best to correct your mistakes.

I hope that you'll be able to clearly get what you want now, no whining attached.