Tell the truth, but not the "complete" truth. You can tell your boss you are getting a new offer with better future prospect and learning ground. What i mean by "Complete" truth is like you are getting higher pay in other company, your current job/company/boss face/colleague/salary is sux, and etc.
Say thank your to your boss, for giving you chance to work at the organization. Tell him that although it is a short period, you have learnt a great deal of things. All the helps are appreciated and will keep to your heart all the advices from him/her.
Inform your colleagues one week/month before you leave, so they can prepare and take over your job. Of course, you can choose not to tell anyone, and quietly sneak away on your last day, but this will leave shock to your colleague, create a bad impression to yourself, makes rumour that you are sacked/not performing well, and makes the life of the person who is going to take over your job miserable.
By doing all these things, you are creating a goodwill to your boss and colleagues.
Who knows you might need their help again in the future. Do you think your boss are willing to help you, if last time you said his face is like baboon when you resigned?
Your image is remained professional and you can leave with style and head up.