First, you must find a reason not to live. There exists uncountable reasons but you must choose at least one and try to make it as ineffable as possible so the people you leave behind may feel suitably at a loss for words when they find you. An added benefit: it will be easier for the people who attend your wake, interment, scattering of the ashes, memorial service, whatever it is it will be none of your business, to speak in hushed and reverent tones if they find themselves capable of speaking at all. Amongst the reasons not to live you might choose: you are suffering from progressive melancholia; by ceasing to exist you will bring your existence to the attention of the person who barely knows you exist, though you maintain a unique awareness of said person’s existence; pondering the great nothingness of everythingness has inverted your thoughts into a perpetual retrospective arrangement.
Compose a note to be found suitably near your corpse, but not in a place where it might slip beyond a finder’s field of vision. Clutched in the hand makes for great cinema and literature, but rarely works in real death. Include in your epistle a précis of your reason not to live. Ask somebody to be kind to your surviving pets.
Leave something in a book marking a particularly resonant passage or one which will send the finder harkening back retrospectively upon discovery. You may choose to leave something in a book at a symbolic page number. One might even leave something in a book which will send the finder to something left in another book which will send the finder to more books always to the last term of the preceding series even if the first term of a succeeding one, originating in and repeated to infinity. Possible items to leave in books: puzzle pieces, scraps of a shirt, pages of other books. Possible symbolic number: 1132.
Select your method of life removal according to your own levels of drama, squeamishness, accessible materials, pain tolerance, or desire to leave a nice looking corpse. There is no need to be elaborate: if you are already poisoning yourself slowly with something, increase the dose; if you tend toward recklessness perhaps walk closer to the cliff edge until 32 feet per second per second takes care of the matter for you; have the light at the end of your tunnel be an oncoming train, or if your perambulations bring you near an oncoming Jagannath: toss yourself into his path. You’ll receive an added bonus for that last one.
If you have items locked away, say in a drawer, leave a key handy or better still, unlock the drawer before your demise so the living won’t have to destroy the furniture to access its contents. It’s just common courtesy. Now go.