Show them the money
If your particular work or ideas have brought the company lots of money, show your boss the proof. Example a woman worked for years for a music school giving singing lessons. However, the academy decided how many students each teacher could take on, so the woman’s income was greatly determined by the committee. When she wanted a promotion to be on the board as well as being a voice coach, she showed the board proof of all of the new clients that had come to the school specifically because they heard how good she herself was at teaching people how to sing. With those numbers proving she had tactics to bringing in more clients, the woman was made vice president of the board.
Create the job you want
Maybe the skills you bring to the table are very useful to the company, but don’t fit your current job description, but you’ve been putting them to use anyways. Explain to your employer how a new position, created just for your skill set, would benefit the company. It demonstrates that you closely evaluate the company’s needs regularly and it lets you stay away from the word “promotion.”
Ask at the right time
Your boss arrives at work already with a full workload, full schedule and head full of worries. Your rushing up to him as he is hopping in the elevator to say, “I wanted to talk about a possible promotion” just makes you another problem he has to deal with that day. Wait for the opportune moment, like at a casual office party where your employer is feeling more laid back and enjoying a glass of wine, or as a business dinner is winding down. Everyone is more receptive to new ideas when they are feeling laid back. Think about yourself when you’re in a rush to catch a bus and somebody tries to talk to you and you get so annoyed. If you are taking a relaxing stroll down a shopping street in no rush at all, you’re more open to hear out somebody who approaches you to talk.
Learn whatever you need to learn in order to fulfill that position before asking for it. If you need to master a computer program, speak a second language, get a certain certification, do it ahead of time. This makes you practically a shoe in for the job as no time will have to be spent on training you or integrating you into the position.