Unfortunately the best way to get space on the iPad is to delete stuff
DOwnloaded content can be deleted and always redownloaded later....for example you can delete a movie, get a few gig back and always redownload it if you want to watch it later (one caveat being that the content must still be available online)
Are there apps you don't use anymore? If you haven't opened a game or app in months/years, do you still need it?
PHotos....you can always upload yours photos to a service like flickr, then delete them from your iPad. Flickr gives you a terabyte of space so it can be convenient online storage for your material.
Settings, general, storage and iCloud usage can show you what is taking up the most room and you can go from there.
sometimes in. your mail the mail app keeps a copy of all sent mails.....well if you dont need those you can delete them.