I think everyone's different but go based on what the majority say and see how it affects your colleague and see how they react to it. I do like it sometimes when people finish my sentences for me if in really struggling to get it out, just anything to stop the struggle. At the same time, a lot of people prefer you to not finish or interrupt the sentence. The best thing you can do is show that you care and you're listening. I suppose once you get to know your colleague better you'll have a more personalised way to interact with them but for now, this is a brilliant start