First, know your position in the mind of your boss, and also, you can have a self assessment: to know if you can have a longer vacation with a relatively high salary. If you can bring great benefit to the company, you are easy to get what you want.
Second, tell your boss the reason of your vacation, and how long it is. Though most of the companies have a fixed vacation for the employees, there are some positions that can enjoy a longer vacation. Also, if you have good reasons for a longer vacation, tell your boss. Don't tell lies.
Third, if you are working in a large company, you should find the right person to negotiate the vacation time. Just find the person in charge of it. Show your respect to him or her, and tell him or her about your idea of your vacation.
Fourth, don't put forward unreasonable demands, or suggestions about your vacation. Remember, you are not the boss, so, don't seek axe yourself.
Fifth, make an arrangement in advance, and do some preparations in mind. Negotiate with a friendly atmosphere. Sometimes, a proper joke or a humor serves well for your purpose.
Enjoy your vacation more!
