Changing your environment (e.g. vacation trip) often gives you fresh ideas.
Try to meet different types of people in your daily life (NYC effect).
Attend conferences. Change departments at work.
Appear available (i.e. don’t stare at your phone). Be passionate - it can be a magnet.
When you feel you’re at a dead end, make a change. Go on a spontaneous trip! Maximize the opportunities for serendipity.
If you plan your whole life, by definition, you can’t get lucky. (Joichi Ito)
If the only people you’re meeting (e.g. lunch, etc) are planned, you are not being serendipitous.