Belhaven Bay is approachable from 2 directions. From John Muir Country park or next to the chalets. Just after Belhaven Bay caravan park there is a small road to the left. At the chalets is a small car park which leads to a foot bridge which is not accessible 2 - 2½hrs either side of high tide. However this is the preferred route by a lot of kiters. (Long walk of shame has been known)Timetable helpfully placed on bridge.
From John Muir Country park it is a fair walk over the dunes before reaching the beach.

The beach itself is over 1km long and best in North - easterly winds. Any direction is usable but can be gusty offshore ie. Anything with Southerly in it.
The beach is normally rippled with a hard flat area near the water edge at low tide.  Beach can be very soft away from the water edge.

There is a dedicated site for Belhaven Bay which sets out guidelines that have been discussed with locals and the council / ranger service. Mainly common sense. http://www.belhavenbay.org/content/