Write down all ideas that come to you over the course of each day. Often your best ideas will come in the middle of a conversation or while you are walking down the street. If you don't have a place to write down your idea, you may become distracted and forget a very valuable idea.
Ask yourself and others what problems they have or what inconveniences them. If you think about it, most inventions are things that make doing something easier or more convenient.
Look at ways other people solved the same problem in a different field or type of product. Look for solutions to one problem in an area that is far removed from the problem you are working on to get a fresh perspective.
Focus on a specific area. The more specific you can be with the type of invention you want to work on, the better your results will be. For example, instead of trying to invent a new kind of lamp, invent a type of switch that can be turned on and off with a clap of the hands or with a person's voice.
Take a random object from around the house and make a list of all the problems or inconveniences that come with the particular object. If you do this with multiple objects you may come up with a common problem or a solution that is present in one object, but absent in the other. For example, you might have a car with heated seats and cup holders but your couch in your living room does not have either of these features.