This time of year (fall and winter) finger mullet are usually plentiful in the surf.  The mullet can usually be found in fairly shallow water, depending on tide and surf conditions.  As you can see in the above picture, the mullet can sometimes be found in water less than ankle deep.  The mullet are all heading south down the coast. 
Sometimes when the tide is high or lots of predatory fish are about, the schools of mullet will be visible out in the surf, but too far out to reach with the cast net.  But even on these occasions, some schools get washed in by the waves, to within reach.  In the picture above, I was standing in ankle deep water, watching just below the surface for for schools of mullet.  I guess I was seeing about one large school of mullet every fine minutes on average.  I was standing with my cast net ready, and when I spotted the school  of mullet, I tossed it in their direction.  We caught more than enough for bait, and I put a few quart bags away in the freezer, for later use.  It really is as easy as it looks.  I learned to throw the cast net by watching Youtube videos and practicing throwing the cast net in the back yard. I use a net with a 12ft diameter.