A bit of an indicator where the high tide mark is on the day is where the seaweed line is left at the base of the sand dune by the boat launching hole. You tend to park between it and the end of the same dune where it meets the main inlet and the "No vehicles beyond this point" sign.
The inlet which is at the very end of the Sandy Pt road sweeps to the left to enter it, if the tides right in you can only drive up to the tree opening where the road meets the sand. There is a high tide car park off to your right as you come off the bitumen with 2 tracks, the one on your left (100m) will take you to the BBQ that faces boat hole, the one to the right (~350m) takes you around to the mentioned dune and boat hole launch area. Tend to only use this on the highest of tides.
The sand can be soft by the waters edge more so where it moves a lot on the banks of the main tidal stream, it's quite firmly packed though for the perimeter where you drive in and park at the base of the dune/foliage. The tide can come in quick when your having a good time, or you break something and get stuck, it can be a long wait to get out again.
NW can be sailed in the inlet as well, with stronger more consistent wind found in the channel that leads upto to the northern end of the inlet towards the Yanakie caravan park. Beware of flat weed banks that are forming out from the east bank SE of where you park also. Otherwise hit the surf in a NW off the shops or at the other lookout ("Ned Neale's") carpark at the west end of town. Or if it's got more west in it head further around Waratah bay (same beach) by exiting town and taking first left a few Km's out where you hit the back of the dunes at the first car park known as "The Gap". There is another spot further west about a Km also, both are good choices when Sandy point is closing out around mast high, it's all sand bottom except for Chicken Run further west along beach from last spot.
Sandy is a great spot to learn the wavesailing when it's small, the waves tend to crumble and tend to be flat.
Goto to Wilson's Prom to take in the scenery if conditions are not right and you have time to burn and places to see.
If you are sailing the SW inlet bank more so, always beware of others sailing around you and take a look behind yourself before gybing. Do not assume your miles out and front of anyone else and gybe, alter course, freestyle etc without looking first, this is key for your safety and others.
Some pics from around 2007, with a king tide and and the state of the smaller dunes that are now much bigger along the SW bank with the ocean in the background breaking through. Wavesailing off the shops/lifesaving club, no need for boat you can fish from your car, and the inlet the way it was back then...