Be inspired yourself. If you're uninspired, think of something to lift your mood - eg, memories, people who inspired you, music, fictional characters. If you're low, don't try to inspire others - it won't work.
Set the mood rather than being led by it. Be more energetic, more controlled, more measured - or whatever you think is needed to establish and maintain an inspirational mood.
Use language that is passionate and expressive. Give answers that provide more than what is needed: 'An excellent book - it was practical as well as an easy read', rather than 'Yes, it was fine'.
Frame what you say in a positive and constructive way, even if what you have to say is negative: 'It was a difficult meeting but a useful rehearsal for the ones that will really matter.'
Have a reason that goes beyond achieving a target. Giving people great holidays is more inspirational to a tour operator than meeting his/her sales objective (although a bonus for hitting the goal may motivate too). As individuals, we need a reason or purpose beyond targets to inspire us.
Focus on the future. If you refer to the past, do so to draw lessons that will help achieve a purpose. Don't use it to point out mistakes, or hark back to better times.
Smile, laugh and show your sense of humour - it will help to lift spirits.
Be irreverent. Inspirational people bend the rules and ignore convention. This may upset traditionalists but it will give hope to those of us looking for a better way.
Keep it going. Inspirational people are inspirational all the time, not just when they want others to change.