Is your problem that you are too shy or that you're having a hard time thinking up new and interesting things? If it's the former, then I'd suggest simply being patient and taking your time. Push just a little bit, then a little bit more, go as slowly as you need to. It's not just the sub that requires some security and patience.

If it's the latter, visit the library on this site! There's so many ideas in there, you'll never have time to try them all.

Some other things: Don't push yourself into this if you don't want to. Don't feel compelled to do things when you don't feel like it. Save any sexual activity for when you feel horny. Make sure he understands that you enjoy it. Worry is a big turn-off. Talk about anything that worries you and talk with him to make sure nothing is worrying him.

I hoped that helped some. Lots of luck to you.