Get a singing teacher would help you alot. They could help you to achieve what you want.

You practice singing by doing exercises, scales and songs. You could probably find some on youtube. A piano is generally used and the aim is to hit the same note with your voice as the piano. Practicing singing songs without lyrics on the recording or someone else singing along with the piano helps you know where you are going right and wrong. Get some sheets of music and someone to play the music for you and practice that way. Read the notes and the words.
Your voice will get better by doing more exercises and singing more. In reality some people just dont have great voices so although they may do alot of practicing and trying to get better, some people still wont sound good.
Ya singing teacher or someone musical with a good ear will tell you if you are practicing properly in order to achieve your goals. To help you at home if you cup your hand and place is behind your ear, this helps you to hear yourself better when you sing.
You can always have a go at singing any song you like, but we arent all mariah careys so its good to push ourselves and try harder things but not to go for something massive. Even some of the best singers fail to do an amazing job of some of the biggest songs of all time. Some notes will be too high, but thats where practice and doing scales come in handy. The more you do it the higher the notes you will be able to reach.
After all the practicing you can feel a bit more confident with your voice, you could join a choir, band, rock it out at karaoke bars, entertainer. Its limitless.

Goodluck with it all!

Hey there!

Well you should practice some scales, they're good for warming up. Can you play piano? If not head on over to youtube and you'l find plenty of vocal scales, you could download some (listentoyoutube.com) and put them onto your hard drive or MP3 which may make things easier! The good thing about scales is that although they are tedious they help you retain your range and perhaps even extend it. They're also great for note association so that once accompanied you'll be able to hear the notes you need to sing a lot more clearly! 🙂

I also recommend singing along to everything and anything you like, whatever genre of music give it a try. It's great to experiment with different techniques you may hear in others voices, some sing from the throat, some the tummy, some have a bit of grit to their voice, some sing incredibly low, some sing like angels! It's a lot of fun to try and emmulate the greats before you, dedicate some time to it. It will help you with being able to sing in many different ways and you'll probably find some techniques that make you sound good and are comfortable to sing. You may find the voice you love the most is your very own.

Best wishes!

Practice singing 1-2 hours a day at least 3 or more days a week. Drink 8 or more glasses of water a day. Demi lavato's sky scraper is a song I saw someone cover on youtube and it's a good song to cover. Always do a vocal warm up before you sing. The songs you sing should be within your vocal range.