Hi, I have trouble seeing when a comma is necessary for situations like these. What are the guidelines (if there are any)?

1.A diagonal line goes in a downward direction, for example (comma here???) from one little corner to another little corner.
2.Those on display are things you wear, for example (comma here?? I don't think we need put a comma - why not?) shoes and slippers.
3.He has a lot of things to do in the morning, for example (comma here??) sweeping the floors and organzing the messy garage of his.
Formally speaking, there must always be a comma following all of these: namely. that is, for example, i.e. and e.g. In addition, they should be preceded by a punctuation mark, though not necessarily a comma.