what is your setup?
some more questions. start with the performance- is it a punchy performance?
then to mic technique, is the vocalist being consistant as to distance and direction to mic?
then to mic choice? what mic are you using? a nice punchy dynamic mic helps for this sort of sound.
after all this, if you still arent getting a punchy sound, there are a million more techniques...
but try the above first.
i have found that lots of vocalists just cant give a good performance to a big LD condenser behind a pop screen. they get timid.
in this case i give them a nice handheld mic with a wind screen and tell them to eat the mic and run around and do what they want, just like at a club. ive been loving a beyer m201 for this purpose right now. it has tons of top end, so the windscreen doesnt cut out too much. and it is very beefy. a beyer m88 would also be perfect for this.