I am a Gem. For starters, you want to seduce them via the mind with wit and clever conversation, or unusual but titillating questions. Personally, I love talking about relationships in any form, so if someone asked my opinion on this-and-that about a relationship, I'm hooked. They're also very physical creatures and love touching and to be touched, so mix that in soon.
Keep them around IS hard because they get bored easily and look for new things to stimulate them. If you're in a relationship with a Gem, endevour to have experiences with them, ie vacations, seeing new things, checking out new places, etc etc. Keep up a good variety in the bedroom and keep them guessing. Gems aren't attracted to drama, but they are attracted to positivity and nurturing.