Wave sailing is good at Umina Beach in a southerly, S/Easter, S/Wester (mostly onshore). Also good at Toowoon Bay in a southerly (side-shore). Kiters are also present.
Forrester's Beach is only really good in a N/Easter. Bit tricky getting out so not recommended for a newbie. Not many N/Easters predicted lately.
Flat water sailing is good at Koolewong (most directions except westerlies) and Green Point (both on Brisbane Water). No weedie needed. Further north is Canton Beach (flat water) but you will need a weedie. Booties also recommended at these locations.
Your combination of board/sail and your ability level should determine where you go.

Good sailing.