No it isn't hard. No you do not need to be a great after dinner speaker, or Churchillian orator. You will be taught appropriate techniques to deliver ground based and flying based teaching. The course will also get you thinking about your flying in greater depth, and as a side product your will find your own flying is likely to improve.
The only caution I would offer is that you should have a desire to teach. In theory you will be assessed prior to undertaking your FI course, by the instructor who you choose. In practice I doubt whether many candidates are rejected at that stage.
Good luck.