It all depends how long you have been practising for. I am a great believer that practice makes perfect when it comes to Su Doku. My first 'easy' took me about 20 minutes and now I have it down to less than 4 after a lot of practice.
In my opinion there is no better way to practice than do 1 or Su Dokus a day, maybe the ones from the Times, as there are 2 each day (On Mondays and Tuesdays there are fairly easy ones). In addition to that, have a look around this site, picking up tips from everywhere you can, and have a look at Simes' and AngusJ's websites, which are useful for learning the techniques.
Hope this helps,
George