This is a bit of a general question :) but

 From:  Michael Gibson
5009.3 In reply to 5009.1 
Hi Steve, also another general tip for making things more friendly to booleans is to avoid positioning 2 objects that are being booleaned in such a way that they have coincident surfaces between them that are barely skimming over the same surface area.

That makes the intersection calculations a lot more difficult for the booleans to figure out.

Instead of having barely skimming coincident surface areas, try to position objects so that they actually punch through each other by a little distance.

- Michael