do offhand

ad-lib devise invent

dash out improvisate knock off make up play by ear toss off

plan prepare read rehearse

ad-lib brainstorm concoct contrive devise dream up invent throw together

coin extemporize fake jam spark

dash off do off top of head fake it improv improvisate made do speak off the cuff wing it

design plan premeditate

ad-lib concoct devise do off the top of your head fake it improv invent make do make up play it by ear speak off the cuff throw together