'How to be vegan and keep your friends' is the actual name of a book.
99% of the time a declaration of veganism is met with ridicule and disdain.
I am not ready to transition to veganism just yet. But I want to make other vegans feel supported and appreciated. How can I do this?
I have many vegan friends and I think it starts with working on your communication and being accommodating. By communication, I mean the culture of people making fun of vegans or perhaps groaning about having to eat vegan food during a night out with friends. This behaviour can be really hurtful for your vegan friends, and just avoiding this completely and even standing up to others who make fun of your vegan friends is a good step.
When you make the person feel that their choices are valid and eat vegan with them during a meal, choose a vegan restaurant, or make special arrangements for their dietary preferences, it goes a long way to show solidarity. I don't think any of your vegan friends will expect you to turn vegan, but being accommodating will be appreciated. However, as a non-vegan I must say that my knowledge is limited. My biggest advice - though it may seem obvious - would be to just ask your friend what behaviour they would like to see from you! Maybe some unconscious mistakes you can avoid, or proactive behaviours you can adopt. Understanding another person's needs always goes a long way. I am sure your friends will appreciate that you are making the effort to learn and grow instead of being ignorant.