I am definitely not what you would call an ‘off-the-cuff’ DM!
The happiest DMing I do is when I’ve prepared well, both in terms of the session that I think I’m going to run, and for those parts of the session that I’m not really expecting to happen, but that might crop up if the PCs go off-piste. If I’ve done this, I’m generally pretty flexible and let the game flow; if not, I’m more likely to try and keep the party on a certain path.
I’ve just got back into running the Amber Pendant campaign, a solo campaign with my son, following a long (almost 2 years) hiatus due to many life things, including GCSE exams, as discussed here. This campaign has always had Icons, even when we were playing 4E. However, on re-starting this campaign, we’ve decided to convert fully to 13th Age. So how do I reconcile the improvisational concepts of 13th Age with my need to be prepared?
Well, I simply take the designers’ advice on p179 of the core rules: If you aren’t entirely comfortable improvising on the fly, consider asking the players for story guide rolls at the end of the session to prepare for the next game.
This suits me much better. I have found myself mulling over the Icon rolls for several days between sessions, and this has lead to some interesting changes in the encounters that I potentially had planned for the next session. For example, we had a ‘6’ roll for the Twilight Lady (an Icon in my setting somewhat analogous to the Elf Queen) at the end of one session. The next episode was planned to be a dangerous trip downriver, with goblins ambushing the party with war canoes and archers on the shore – how could that relate to the Icon in play? Eventually I struck on the idea of a fey giant turtle surfacing from the river and aiding the characters (as the advantage conferred by the roll). This turned out not only to be a cool addition to the encounter, but also quite necessary to stop a potential TPK … as the battle was pretty vicious!
I now try and make notes in the planning for my next session as to how the Icon rolls (if any) will impact the session, as shown in this snippet (from my Scrivener campaign workbook)
Originally, this whole episode was not even envisaged … but once I had the roll to work with, the creative juices started flowing…
Until such time as I feel more comfortable with an improv style (i.e. not very likely …), Icon story guide rolls at the end of an session or episode is definitely going to be my method of choice 
