I was pretty impressed with this weeks Game Master Tip on the Mary Sue with Wil Wheaton. For one thing, as much as possible I believe saying “Yes” to whatever crazy plots or similar your players come up with is rather important. When you do so, it help your players feel like a part of the world and show that their ideas are being validated. A good example of me improvising on the fly like this was with the safe house security features a player came up with in the Night’s Black Agents one shot, Nightfall.
I was particularly enthused with how far Wil went with this, when he actually modified the rules for a druids companion animal from another system (DnD?) to provide Aankia with her robot pal, Jeremy. Most importantly, he did so in a way without complicating the game in any extraneous manner – adding an NPC to combat is always problematic – and by providing interesting choices for allowing the player to have it.