If you want to induce a lucid dream by external methods, do the following:

Note: Be sure to do this on a night you can sleep at least 9 hours.

1) Buy a vitamin B-6 suppliment.
2) Set your alarm to go off five hours after the time you are going to bed.
3) Set the B-6 and a glass of water within reach of your bed.
4) When your alarm goes off, take the B-6 and about half of the water.
5) Lay back down.

You will immediately fall back asleep if you have not turned on any lights or stirred much. Try to focus on a bridge object (see my other post on this topic), or use the MILD or WILD techniques.

Word of Warning: Excess amounts of B-6 have been found to have neurotoxicity. Do not do this often. The goal is to have lucid dreams naturally, by intending them, and not with the aid of a crutch such as B-6.

SubNote: Bananas are high in B vitamins. This is why people say eating a banana before bed can cause "nightmares." The reality of it is they are just aware of their dreams more. This usually frightens people who are not prepared for lucidity, since they are not expecting it.