To become a professional singer you need to be really highly motivated. Your whole heart must be in this profession, because you need to work very hard. You will have to push for your creative vision, and they will surely reject you many times before you “make it”. However, I am sure that once you reach a certain level of success, you will feel amazing. Get ready because this will be long.
Steps

Step 1. Make sure this is something you really want to do
Not because of fame, but because you have a real passion for music. You are going to need a lot of hard work.

Step 2. Take singing lessons
No matter how talented or terrible you are at singing naturally, the classes will teach you a lot, and help you improve your voice.

Step 3. If you want to be in a group or a band:
You need to look for dedicated musicians who have the same creative vision as you, and who you feel comfortable collaborating with. If you pick the wrong people, you can get into serious trouble along the way.

Step 4. Once you feel comfortable with your voice:
You need to get used to singing in front of other people, start singing in front of people with whom you feel familiar and comfortable, such as a school choir, or church.

Step 5. Now you need to start getting comfortable singing in front of strangers:
(1) Go to a local fair and ask if they have open spaces for performances. (2) If there are businesses that have open mic at night, go and sing. (3) If you are lucky and you live in a big city, you can make your presentations on the street, or perhaps in a public square.

Step 6. Optional:
Make contacts! This may not work very well if you live in a small town. Make friends with the people you meet at concerts, you may end up opening a concert for a "bigger" band, and thus get more contacts.

Step 7. Start recording your demos
You can even use a program called Garage-band on a Mac.

Step 8. Start promoting yourself like there's no tomorrow
Tell your friends, family, make flyers to promote your concerts, make a MySpace account, a Facebook profile, Twitter, a YouTube channel, anything you can to get your music to more people.

Step 9. Send your demos to record companies
Don't be discouraged if you are rejected, keep trying! And remember, record companies DO NOT want to hear something that has already been done, be original.

Step 10. Keep going
Keep giving concerts (go on tour if possible), promoting yourself, submitting demos, and growing your fan base. Companies like to see that you are taking the initiative.

Step 11. Once they sign you:
Don't let the company control the way you are. Fight for your creative vision, because if you don't, well, that won't be good …
Advice
- Don't do this for money, do it because you love to sing.
- Be patient!
- Don't let anyone try to stop you. If this is what you really love, then do it. Don't waste your life dreaming "what would have been …"
- Get a representative. Some companies will not let you send them your demo unless you have a representative.
- Some companies only listen to the first 30-60 seconds of a song. If they don't like it, you're out …
- Make sure that when you start working with other people (manager, members of your band, etc…) they are dedicated and respectable people. If not, you will surely get in trouble.
Warnings
- READ the contract before signing with a record company.
- Don't fall for scams! You shouldn't be paying money to anyone until you start making money.
- Get a good singing teacher, otherwise you may spoil your voice.
- If you don't fight back, the record company will control you.
- Don't get your hopes up, work hard.