Then the basis of steampunk is the victorian style clothing, it is the details that transform an outfit from an old fashioned costume into real steampunk. If you are a man you can choose the pants matched with shirt and vest. If you are a woman, you can choose the corset and the dresses which similar to the victoiran dresses but with a more copper or brown color.
The main DIY here is the accessory part. This is the most important factor to make you look different from the others. So add some metal tones. Part of what defines steampunk is metal accessories that invoke the industrial revolution. Use gears or other bits of metal to make jewelry or other accessories.
Through what I mentioned here, you will have an authentic steampunk look all by yourself. And this will look definitely different for you from the other people.