If you are thinking of making your own rubber stamps, I would say a good shape to start with is a teadrop. It is easy to draw, easy to carve and very versatile. So far I have used it for the petals on the flowers on this wrapping paper (stamped onto normal brown packaging paper from the post office) and as balloons on this birthday card. Obviously they can also be used as raindrops; I’m thinking of doing a big silvery cloud with rainbow coloured droplets falling from it. If you’re doing a flower with a stem you could also use this stamp for the leaves. The opportunities are endless!
I also found a really nice blog which has lots of tips and inspiration for creating your own rubber stamps. Start here but check out the rest of her site too.