For mackerel, I found little mackerel feathers like:
That works well. You have like 5 in a line about 10cm apart, with a small crush on lead weight so you can cast it.
High tide is better for mackerel if casting off the shore.
A nice calm walm evening will see them come into the shore chasing sprats. Look for where the seagulls are going nuts, thats usually were these little sprats are. You can often see mackerel bubbling / jumping on the surface.
You in Plymouth still? Maybe try that wall near the wet wok / fish resturant on the hoe, seems pretty popular with fishermen there.
Good luck!