In principle, a LEGO bracelet is simple - drill a hole in 6 bricks, and thread elastic and/or string through them all.
There are two ways of drilling the holes. The first method is to drill a hole in both the top and bottom of the brick, and thread the string over the small divider in the middle of the second. This is the most accurate, since you centrally align the hole on both sides. However, the threading is more complex.
The second method is to drill all the way through the brick, including the three connectors on the underside. This is less accurate, and more difficult to drill, since you must hold the drill perfectly vertical to ensure the exit wound is centrally positioned.
To expedite the process I took the second approach. To make the threading easy I used a 4mm drill which is large enough to thread the string without problems, but so large that it decimates the internal lug holes.
To protect the bricks I first trapped them between two flat bricks. This also allowed me to drill three holes in one vice operation.