Wish I have an answer... mostly, the product and the company. If the product excites my imagination and I trust the company, there is a good chance that I jump in.
It is very, very important that the people after the KS keeps a good communication, show enthusiasm and regular updates. Good photos of the product are really helpful.
Also, shipping costs and potential taxes have an impact in my decision. It is more probable that I jump in a KS that is EU friendly than in one that it is not.
Rewards are enticing, but they must be really interesting to have a meaningful impact in my decision to participate.
Finally, I appreciate when the company makes a honest assessment of the risks involved and, specially, the timeline. I rather prefer they tell me that the product will be received in one year after the end of the KS, than it will arrive in July and then don't receive it until May... next year!