It's not my diagram - just an example from Wikipedia so I am not sure how they used them.
Usually I find colors most important e.g. red arrows for conflict or green ones for friendship. Especially for the ellipses: here again red for opponents, green for friends, gray for neutral, blue for players. Other things I use: Size of the ellipse for importance. Dotted lines for loose connections, big ones for important connections. Arrows only in one direction means one-sided relationship.