I like to think of time as a river. You're a particle floating down the river. Pick you up and move you upstream, and you'll still pass through the same moments in time, but you won't affect the water you used to be in. Cut the whole river off with a dam, and all the water downstream of the dam continues to flow (please, no one talk about turbulence and fluid dynamics, you'll ruin the illustration).

Go back in time and change something -- you'll change it for you and everyone else that exists at the same time as you, but for those in the timeframe you came from there will be no change, except that at some point in time you disappeared.

The most effective way to clone yourself from your own perspective is to go back in time a few seconds and then stop yourself from going back in time again. Voila! There are two of you! But at the cost of your existence in the time-frame you originally left -- you can't say to someone "Watch, I'll clone myself!" As they'll see you leave their timeframe and never come back.

Well, if time travel was to happen that's how I would imagine it.

Jibb