Pick your moment and be positive! The morning of an important presentation isn't great timing. Schedule a private meeting with your boss and tactfully talk through the reasons for your decision. Be appreciative of the skills you have learned and thank your employer for their contribution to your career.
Don't include personal remarks in a resignation letter. If you genuinely have differences of opinion with your boss, keep any negativity to yourself - and never commit thoughts to paper - your comments will remain in your personnel file and may come back to haunt you.
A hand written note to your boss thanking him or her for understanding your position and perhaps offering to be available by phone for a couple of weeks after you've gone can go a long way to softening the blow - and will be remembered when it's reference time.
You must be prepared to actually leave. In other words don't use the resignation as a threat to try and get more money, benefits, a promotion etc - it will almost always backfire. Even if it works in the short term, your card will be well and truly marked.
Don't be tempted to tell people what you really think of them. You may want to return at a later date; you'll want a good reference and colleagues could well end up at another organisation - one that you may be looking to join at some point in the future.
Give at least the notice that you are obliged to give, plan your workload for your notice period and carry on working as normally as you can - it's very easy to become de-mob happy and more relaxed about the hours that you keep but it's not the mark of a professional.
Don't leave projects unfinished and agree handover periods so that the company is not disrupted by your departure. Offer to help in the search for your successor and if a suitable replacement is found, be as helpful as possible in terms of answering questions and assisting with training.
Don't get caught off-guard - particularly if you are leaving to join a competitor and you think your employer may ask you to leave as soon as you tender your resignation. So there's no question about what belongs to you, prepare by removing all personal items and files from your office and computer.
Take the time to speak with your colleagues -and make positive comments about your time at the company - and their contribution to you. Get contact details for key people, tell them you'll stay in touch - and mean it - your paths may cross again and it's always good to network.
And finally Don't jump the gun. Never resign until you have a solid job offer in writing. There are countless stories of employees who've resigned based on verbal job offers that later fell through. A verbal job offer isn't worth the paper that it isn't written on!