Playing lines in a position

It's not often the position is completely foreign. So when finding moves "on the fly" you still have some points of reference.

Other than that, basic good things like space, piece activity, coordination, king safety, pawn structure, and all that.

My best on the fly improv has been to actually stay in book for many moves lol :) So nothing too spectacular (but not bad either of course).

Maybe the most funny was I played into a mainline closed Ruy... and came up with an amazing idea... to play Na5 followed by c5! I reasoned I should play on the queenside, and that c5 not only gained space, but got rid of the potentially backward pawn, and maybe I'd even get to play on the c file! I was really proud of this idea and asked my opponent after the game what he thought of it...

All of this of course had been played many thousands of times over at least 100 years 

That's awesome! I am not sure how I want T go about learning the book lines. They look fun! So far i am learning responses to 1.E5 because it is one of my favorite moves but I like 1.D4 too! I am just picking some lines and ideas that I think would be fun to play out of. Now if I run into a position I dont know, I may be in trouble! But I guess that is the fun in chess!