Try to find a good time to ask for a raise. Here are few examples of good opportunities:
1. Obviously, the opportunity for a raise should be ripe during scheduled performance reviews. Use these opportunities to enumerate the reasons why you should get a raise.
2. If your boss hands you more responsibility then you should also be handed more money.
3. If business has been good for the company then the boss has more leeway to be good to you.
4. Ask for a raise immediately after orchestrating a successful venture.