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Just going to my classes. I know that this sounds silly and I am sure you are doing this anyway, but try and make sure that you are going to your lectures and seminars as they are great ways of making friends, especially if you have any group work or you do any group tasks in the seminars. Try and speak to a new person in one of your lectures and sit next to someone new as you never know you may get on well with them.
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I know you said you are unsure about societies which is fine, but there may still be something that you enjoy. They aren't all as scary as they seem and some have less members which might feel less scary. Or, if you don't want to join now, you could join next September as there will be lots of people there then which are new so it wouldn't just be you!
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Social media. Sometimes on social media there will be groups where you can connect with people who are on your course or just at your uni in general and this can be less scary than talking to people face to face. It's worth having a look as you may meet some people this way!
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See if your student union puts any events on. Often the SU will have events which you can go to - at Hallam the SU puts on 'give it a go' events where you can meet new people and try out new, fun activities! It's also worth a look as there may be something fun you are interested in.