I’d suggest finding lyrics you can associate with, or relate to, and sing those – the added emotional attachment you’ll feel while singing them, will help you sing without attempting to sound any specific way – giving you “your own” sound. Also, rather than sing along with the vocal version of the songs, try to find the instrumental – or even karaoke version. That too, will help prevent you from trying to sound like someone else. The less you try to sound like the song/artist, the more you’ll sing with everything you’ve got – thereby strengthening your voice just by using it fully. :)