Information Overload...
So, we all have our crutches to help us know when to shift, right? RPMs, throaty sound of exhaust system, MPH, etc. (all great suggestions, by the way)
Still, to a person new to manual shifting, this all can be intimidating, fostering more fear than the good intentions it is meant to offer (when everyone tells me how easy bungy-jumping is, I tend to still question whether or not it's for me).
I treat manual shifting like
potty-training. The best advice for potty-training is to not take any advice on potty-training as it will only frustrate when your child doesn't match up to what the books you read or others tell you.
Rather,
just do it and find what works for you. The
smart has no clutch and will shift for you in manual mode when it's limits are reached, so there is no need to fear you will damage anything.
As you play with it, you'll figure it out
Now, once you hurdle that first hump of adoption (and you're shifting like the best) the advice from others in this post can most certainly help you
refine what you've learned to optimize for mileage, sensation, or performance.
Besides, you'll find that it's really fun!