Look at joining the NCMD they have a website that gives advice and tips especially about the legalities of detecting. Plus your membership covers you for liability insurance.
Beaches are a good starting point,you can detect without a licence on crown estate beaches there is a online map.
Look at joining a local club they sometimes organise club events.
You have to have permission to detect pretty much everywhere else than a beach. I have been detecting for a couple of years but I'm down south.I did manage to get a permission to detect on a field near Lyndhurst in the New Forest.So far found a lot of horse related stuff and some military.I suspect the field was used as an army camp during both World wars.
The ground is too hard at the moment so I will probably hold off till the autumn before I get back out.
