If you are serious about becoming a really good singer nothing can replace the one -to-one exchange that occurs in actual voice lessons

A good singing teacher can help you in many ways. 

Regularly scheduled lessons.
This allows you to set goals and progress. You have a plan!

Someone to hear you.
You really cannot hear how you sound to others.You need an experienced voice teacher to help you produce good focused tone,pitch, diction and vibrato.

Expansion of your repertoire.
A private voice teacher can introduce you to a whole new world of music. They can choose songs and exercises suited to your individual vocal range and abilities.

Networking with other singers and muscians.
Your teacher will probably know how to link you up with other musicians in the area

Development of other musical skills.
A good voice teacher can incorporate music theory,listening skills and keyboard into your voice lessons. The more you know about music in general, the more grounded you will be as a singer. This will give you an advatage over others without this training

Resource for further study
A private teacher is connected to local educational institutions will know about local classes,workshops,auditions,conferences and concerts that can greatly enhance your study of singing.

Questions to ask a Voice Teacher

What is your professional singing experience?

What is your teaching experience?

Did you study how to teach and if so, where?

What kind of musical styles do you teach?

What is a typical lesson like?

What kind of practice should I expect?

How often will we have lessons?

What other learning experiences can you provide - such as group classes, keyboard training, theory skills?

Who are some of the students you have taught?