We went last summer. Some places on the north coast were very busy, one day we drove through Padstow and didn't bother stopping as it was heaving! Nowhere to park either. Friends staying in St Ives said it was the same there. On the other hand, we stayed not far from Truro and I'd really recommend Falmouth, and the beautiful villages around there. There's various boat trips up the Fal estuary and some gorgeous little seaside harbours. St. Mawes is lovely, we had a novel trip on the King Harry Ferry (very short car ferry on a chain) too and St Just was beautiful to see too.
We did two day trips, both pre-booked well in advance. Tintagel Castle and the Eden project. Had a great time at both. Lots of steep walking at Tintagel, so be prepared for that.
Lands End had to be done but is a disappointment to be honest. Theme park style stuff there, but we've been, it was a fleeting visit! Sennen Cove, around the bay is beautiful though. We preferred Lizard point which is the southern most point in Britain. Went from there up to Porthleven, a lovely little harbour with some nice restaurants and a shingle beach.
St Michael's mount is worth a look. It's only open on certain weeks and you have to book if you want to go. It's National trust. If it's not open its still worth seeing and the town opposite is nice with a good beach.
We wanted to visit one of the mines but they were either closed or fully booked.
Hope you have a lovely time. We're hopefully going to Pembrokeshire this year!