For general walks at this time of year you could try Horner Woods at Horner, near Porlock, walk upstream from main car park area, good chance of wood warbler and pied flycatcher, or try higher up for tree pipits, redstart. Haddon Hill at south west end of Wimbeball Lake, near car park, is also good for tree pipits. Also, Chetsford Water, and Ember Combe for chance of cuckoo, whinchat and redstart. Dunkery area for grasshopper warblers.
Another good general walk is Dunster Beach, and Hawn, best either side of high tide for chance of waders.
Hope this helps but if you require any more specific information please feel free to get in touch.