Listen and keep listening. Find out why they are sceptical so that you can tailor your arguments. Let people talk through their worries first. They'll be more likely to hear what you have to say in reply.
Empathise. Demonstrate that you understand how they feel.
Use rational argument. Provide specific facts where possible. Of the nine major influencing styles, rational persuasion is considered to be the most effective. Psychological experiments show that saying 'because', followed by even the most improbable of reasons, will increase numbers converted by up to 50%.
Let others put the case. It might be that you are the barrier, not what you are saying. Put your ego aside and allow other people to give their reasons. Even if the others aren't as fluent, simply seeing that a number of people have similar views will be persuasive.
Paint a positive picture of a future that the sceptic could enjoy if only they came round to your way of thinking. This will win people over and bring them on board because they pursue the vision you've described.
Give a little. If you show that you can be persuaded, sceptics might be encouraged to do the same. Treat sceptics with respect, not love (or hate). This shows you are confident enough to allow dissent, but it leaves something more for those who come on board.
Leave be the ones that are really hard work - there will always be some. You could be surprised: being ignored may be just what wins the truculent critic over to your view.