How to be warm?

In the past people have considered me to be a cold person and have said I can come across as intimidating but I'm worried that because of this I may not make any friends at uni so how do I become more approachable? And how do I become a warm person? I would like advice that isn't just 'smile all the time' because it would be weird if I do that and on the first day of class I'm not gonna know everyone enough to smile at them so how do I become likeable?

I am autistic and I know that I can sometimes come across as abrupt or cold as I lack the awareness on occasion to fulfil the expected social chit chat. I have a mental checklist that I use when I communicate with people. I always try to remember to greet people appropriately, ask how they are and to take a friendly interest in their lives, listen to what they want to talk about etc.
sometimes I forget the checklist and go straight to the point of the communication eg about a piece of group work etc forgetting all the social niceties. It is not that I don’t care about people feelings etc or that the people aren’t important to me, as they really are, it is that if I don’t always remember that these things matter in friendships and going straight to the point every time it can seem cold or rude.
Making a concerted effort to do this has made me better at making/keeping friends and talking to new people and my friends are kind enough to give me understanding when I forget. The more you do it, the better you will get.
I hope that this helps you

Thanks, I'm autistic too and what you've said has really helped