The first step to fitting in is to get a sense of the culture of your workplace. Every organisation has its own culture, which manifests itself in the dress code, the look and layout of the place, the level of formality and the way staff interact with each other. Getting a clear sense of the way things are done is an important step towards making sure you pitch your own behaviour in a way that will chime with your colleagues. If you show up every day in a suit when everyone else is wearing jeans, unless your work requires it, you'll be erecting a barrier between you and those around you.
Set yourself some basic rules about how you deal with your colleagues. Don't be critical of them or their work. If you have an issue with someone, approach them about it personally rather than airing your concerns with other people, and do so in a positive, constructive way rather than being confrontational. Asking for help with problems you have with your work is a good way of breaking the ice and indicating a level of respect for colleagues' opinions, which will help. Developing these kind of habits will create a good climate for fitting in.
Make the effort to go to social functions arranged through work. These allow you to meet your colleagues outside of the usual working environment, when they're more relaxed and the organisational hierarchies and work-related barriers are weaker, and you can let your personality come across more easily. If you're asked to join people after work or at lunchtime, accept, because that's a clear invitation for you to fit in. And, if nobody asks, it's often because everyone thinks it's someone else's responsibility, so don't be afraid to do the asking yourself. Just like you, most people like to know that others are interested in them.
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