Bit of beach advice???

I'm falling into what I am sure is a great newcomers trap. After casting
about twenty times with a given lure,and having no bites, I stop, change
lure type and start again .

Is this just rubbish practise? Should i set myself out with one lure type
and cast it for an hour or so?

For the record, I was today on one of the bournemouth beaches at high water
for an hour (all i had) and i tried rapala blue J13, orange shads and a
metal thing that looks like a browny silvery fish. No bites.

I also had a weighted one-hook rig with prawn. No takers either.

Observations??

David