If you're close to the city, come down to peli point and meet the crew.
Once the sea breezes start up there's always someone sailing there after work each day, on the 20knt plus days, the rigging area will be full. The rigging area is at the quantas boat ramp, just to the west of pelican point if you look it up on google earth.
I should probably point out that most people follow the wind around the river, so peli point is good if the wind is from the south. If it's a nor wester like what we're getting at the moment Melville beach on the other side of the river is where you'll find everyone (dunkely ave, if you want to look it up...) I'm sure whom ever you come across will happily tell about some more spots, and how to get to them. There are plenty more spots, Melville and peli are just the more likely spots you're going to find windsurfers on the river. Hope to catch you soon