Start with a one and a half or a two. This strength of reed is fine for beginners. Some brands also come in filed and unfiled. The difference between the two is subtle, so experiment to find the cut that works best for you. Do not buy into the common misconception that the harder strength of reed that you play on, the better you are.
Most players use a medium strength reed and a medium size mouthpiece.
If you've heard Michael's playing, you know that a medium reed works just fine for him. Using a reed that is too hard will lead to the very bad habit of biting and your sound will be harsh and out of control and out of tune. Using a reed that is too soft will give you a weak tone, poor intonation and no projection of your sound. First, soak the reeds for about ten minutes in tepid water, making sure to soak the entire reed. Push them underwater to soak them thoroughly.