Keep singing!!! That is one of my tips!!! the more you practise, the better you'll get!
Also, practise scales and warm-ups daily, and every now and then, try to reach a new note - but don't try too hard, as this may damage your voice (if it starts to hurt, stop.). This will increase you're vocal range and improve the overall strength of your voice.
know your strength and weakness....
if you're already good in this type of style then move over to a different exercise. practice things that is hard for you, not those that you are already familiar with.
the best way to improve is to be natural. take it your own pace. learn to stop yourself when its getting too high or low- in time you will get to know your voice and be able to recongnise when enough is enough. you dont have to sing your heart out every day- it does more harm than good- but warn up every day - or even every other day- if you feel like it.