worst thing u can do is try singing along to a good vocalist like freddy! lol
just practise gradually, and ignore the part bout developing vibrato, that will come too. and corn? if u wanted to clear ur voice of plegm and stuff, gargle salt water - tho salt isnt neccessary if ur voice is already quite clear.
the best way is to get singin lessons, or at least by a book or listen to some Mark Baxter mp3 things. hes a vocal coach - worked with steven tyler, thats all u need to know.