Although there is no substitute for upgrading your singing skills than to get some kind of professional tutoring, there are some things that you can do yourself that should help you.
You can develop your own style, for one.
But first, last, and foremost you have to sing on key.
You have to hit the notes.
If you are not hitting all of the notes, all the "style" in the world will not help you to become an effective singer.
Practice singing scales (do re mi...
) and record them.
Then play the recording back and listen.
If you have the talent to sing in the first place, you will be able to tell if you are singing on key.
Work on your mistakes while you are recording.
You're not making an audition recording here, so don't worry about the mistakes -- just learn from them.
Once you are confident that you are hitting the notes, do it again but try these things: 1.
Sing the scales up and down staccato (that is, "clip" each note).
Over annunciate each note.
2.
Sing the scales up and down legato (that is, smooth and run together).
3.
Sing 1 and 2 alternately in the same scale (staccato legato, staccato legato).
4.
Sing 1, 2, and 3 above softly.
5.
Sing 1, 2, and 3 above loudly (but not screaming).
You must also concentrate on hitting each note.
I could also mention "sing from the diaphragm", but that is a touchy subject.
This is more concerned with breathing properly.
A lot of people sing while holding their breath.
"Using your diaphragm" involves exhaling the notes out -- which means at some point you need to, um, inhale.
It's all about breathing properly.
Some kind of professional tutoring may be necessary here.
At the same time that you are doing all of these boring exercises, start listening to your favorite songs and imitate the singing style.
Every nuance, every inflection of the voice -- copy it exactly and precisely making sure that you are also hitting the notes.
Do not choose songs that have a wide vocal range of notes that are out of your range.
Some singers have 2, 3 or more octave vocal ranges, and most of us have no ability to do this.
Also keep in mind that many of these recordings won't be in your "key", or effective vocal range.
You will have to sing them in your key.
If you don't know how to do this, stay away from songs that you are not able to copy directly from.
You don't want to strain or blow out your voice.
If you can do this with enough songs, you will begin to categorize the styles internally.
Then you will start automatically "pulling" these styles out without thought when you sing.
In effect you will begin to develop your own style.
At some point in this process though, if you are really serious about developing your voice for professional reasons, you will need to get professional help.
You don't want to develop a lot of bad habits.
But understand that after the ability to actually sing on key, it will be your singing style that will or won't make people want to sit up and listen.
Singing is about communication.
It is your singing style that allows you to do this effectively.