The way I did it was by deliberately going against my normal impulses. The rule was "whatever you would normally do, do the opposite of that". If you would stay home, go out. If you would eat a steak, eat spaghetti instead. If you would get drunk, stay sober. If you would stay sober, get drunk. Basically, as long as it's not something that's likely to do irrevocable harm, do things that don't seem like good ideas and just see what happens.

The limits on our experiences are usually self-imposed by the fact that we tend to make specific choices limited to specific contexts. The experiences you have are the experiences that derive from what you think is a good idea. So doing things you think are bad ideas tends to result in a lot of new experiences.