Try out songs that are slightly out of ur range, so u can see how u improve.
BUT dont stress ur vocal chords out, its surprising how many ppl strain their vocals, cus they dont sing in their true pitch.
Check out some good websites on finding ur pitch, even actors need to do this to speak in their true pitch, most of the times evryone just acts, in a manner they think best, but is not their pitch, and so they screw up their vocal chords.
A book i know of that teaches u this is 'through music to the self' by erm.........still thinkin......peter or michael or peter michael hamel. The surname is hamel or hammel for sure. hehe [im not home so i cant check]
And i recently had a conversation with a guy who sings in a death metal band and i asked him to give me tips on how to growl, cus i can't very well [and dont tell me women can't cus u should check out angela gossow - arch enemy] anyway he said 'u have to find it urself, theres no way to go about it, it'll come naturally, just learn how to best control ur voice'
so there u have it, as always u have to find whats true in ur heart and go with it, without putting too much pressure and tryign to forget what everyone else did o get there. i know its hard but one thing i can be certain of is that the more u sing the better ur voice will get, as long as u do it propely ie not stressing out, and ull know when u do this cus ur throat will be sore right after, or ull find urself coughing...
long reply,,,i hope u read it all ;)
'i dont have low self esteem, it's a mistake. I have low esteem for everyone else' - Daria