Try these great tips:
1. Offer something in return when you ask for something.
Helping in chores or completing specific ones, or getting better grades in specific subjects something you can always offer.
When you are specific, it is easier to measure the results. Therefore, it's better to say, "I'll make my bed and get up early" than to say "I'll get my things done on time." If you don't do so, you can expect a negative effect. If you actually mean and do your part, you can expect wonders.
2. Give them time to think
Nagging your busy parents for something you want will result a straight 'no'. Rather, ask them to think about it and give the response later. It will give the idea that you're patient and mature.
3. Contribute your part
Compare the amount you have to the amount you need. Show your willingness towards contributing for what you have.
4. Ask with gratitude, show appreciation!
Instead of demanding things like you deserve them, show your parents that you care and appreciate their hardwork.
So, when you need something, show gratitude that equals to the amount you're asking for. Thank them for the things they do and then place your demand. This is not to trick your parents to thinking you care but actually appreciating them. The good you wish will pay back.
5. Earn credit, slowly
When you want little things, parents are prepared to give it to you. But for the bigger things — a car, MacBook Air, Nikon DSLR, etc. — a more deliberate approach and patience is needed.
You will have to set goals for yourself, keep your commitment and do the things you promised you would, or even a little more. This will prove them you are mature, responsible and deserving of it.
6. Make them look good
Everyone cares about how they appear to others, same is the case with our parents. They feel judged about their parenting skills. So, when you hang out with your parents, or are around their friends, be presentable and wear the mature stuff. Talk to them in polite tones and answer their questions interestingly.
Parents will consider you responsible and give a thought to the demands you make.
7. Stage your requests carefully
Setting the right stage for placing your demand increases the possibilities of getting a 'yes'. Therefore, never ask or demand a stressed parent and always make sure they have time.
8. Try to solve rather than create the problem
Think carefully about the things you do. Don't involve in any kind of mess. Always try to be the contributor, the moderator. When your siblings start something, be the one willing to give up. This is let your parents you handle things maturely. This will increase the prospect of getting a 'yes'.