I have a lot of plain bangles for making dream catchers as little gifts, and my friend gave me seed beads for Christmas. Thus, I decided to create a new bangle (even though I don't wear bangles... but I'm tempted to wear this one), and here's how I did it.

Step 1: Materials

two bangles OR thick gauge wire (24 and above)
thread (I used beading thread, but regular sewing thread is fine
beads (Any size is fine. You can always make your own. If your beads are smaller, you'll need more.)
glue
scissors
thin needle (thin enough to fit into your beads) (If you don't have one, be creative! Make a crude one from thin gauge wire or wire savaged from bread ties. Hey--at least it works.)
OPTIONAL: yarn

Step 2: Making Bangles

If you don't have bangles, just make your own from wire. Cut out a piece of wire that it would fit around your hand easily when curved. Then make two loops, one on each end of the wire, and connect the two loops like jump rings. Make two.

If you have bangles, good job so far. ;)

Step 3: Wrapping

If you want to change the color of your bangle or make the next step easier, I suggest you wrap your bangle with thread/yarn (yarn is much easier and faster). To do so, tie a knot (leave a tail) to connect your string to the bangle and begin wrapping the bangle with the string, working with the whole spool of thread. If working with the spool isn't possible in your case, cut out a long piece of string (always overestimate for this; you'll usually need more than you think; use more string if it's thin) for wrapping. You'll need to hold onto the beginning tail (from the first knot) for the first inch of wrapping because the knot will spin until friction is enough to hold it in place.

To finish the wrap, tie the end with the tail from the beginning knot. Seal the knot by putting a bit of glue on it. Then cut the strings off as close to the knot as possible.

Repeat with the other bangle, but THIS TIME:

If you're able to work with the spool of thread, then at the end, make a knot and seal it but DON'T CUT THE STRING CONNECTED TO THE SPOOL (cut the other one only). Unravel a lot of thread (I'd say two full wingspans if your thread is sewing thread thin) and cut it out, making sure it's securely attached to the bangle.
If you can't work with the spool, cut a long piece of thread for wrapping and cut both strings after sealing. But then make another knot with a new LONG piece of thread, seal the knot, and then cut the TAIL STRING ONLY (not the longer thread).

If you didn't want to go through the hassle of wrapping (I don't blame you at all), then make sure that the colors of your thread and the bangles don't clash.

Step 4: Adding Beads

To add beads, I used the ladder stitch. To be honest, I messed up a bit on making a "real" ladder stitch, but everything worked out anyway. Make sure you know what pattern you want the beads in if you're alternating colors. If you are alternating, the end might not complete the pattern you're following (as in if you are doing red green red green, the end might be red red, thus messing up your pattern). Thankfully and surprisingly, mine ended perfectly so just be mindful of this.

Start with your long thread attached to the bangle and string on a bead (string the thread on your needle first). Settle the bead between your bangles and put the needle above your other bangle (no string attached), through it, and then through the bead. Pull to tighten. Then put your needle above the other bangle (one with string attached), through it, and string on another bead. Settle that bead between the bangles before putting the needle above the other bangle (no string attached), through it, and then through the bead. Repeat (and refer to pictures above if you're having trouble--it's tricky at first) until you can't fit any more beads.

Step 5: Finishing

When no more beads will fit, end the bracelet by making knots. To do so, poke your needle into a gap between the beads and then through the circle of thread that the step creates. Pull to tighten this first knot, and make another one for security. Dab some glue on the knot before cutting your string.

Then you're done! Congrats, and enjoy your new bracelet.