1. Fix the lens that is capable of a focal length of 50mm (or higher) on your DSLR body.
2. The second lens has to be inverted. In other words, the front of the second lens needs to face the front of the first attached lens.
3. Now using tape, affix the lenses together. A standard cellophane tape would do, but you can use any tape that can be easily removed and still doesn't leave any marks on the lenses.
4. Switch the camera to manual focus and try to focus on an object by getting in real close. Once you have a clear focus, click and you have your macro shot.
5. If you prefer to shoot on auto mode, then see to it that the first lens has a lens hood, which can be used to fix the second lens onto. This is done to avoid damage to the first lens when used in autofocus mode, since auto focussing usually involves movement of the front lens element (which, in our case, would be fixed with the second).Yet another way is handheld shooting

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Yes! The second lens can be held in your hand and you can still come away with a very decent macro photo. Although this needs practice as slight movement or low light situations might cause the picture to be out of focus. Now this might not be a permanent solution to your macro needs, but it can give a taste of macro photography on the cheap and help you see if it's worth investing in a dedicated macro lens.
Image: maldiviandude