Terracing would help but maybe that's more work then you want to sink into the project. Railroad ties can sometimes be the easier solution.

Here is a link that might be useful: Peropagating Perennials

Use an erosion control blanket over the seed. I did this on a very steep slope with creeping red fescue and it worked out pretty well. As mentioned above, terracing is great but it's a lot of work and/or money.