For me (and also Barry) creativity gets a big boost when we simply get together and plug something in.
Neither of us has a problem coming up with ideas on our own, but when we are both slinging mud at the wall some really cool things tend to happen.
I also like collaborating with others, as mentioned above, especially with people I'd likely never have met otherwise (Limey, Jazzmandan or MusicStudent, TommyC etc) That is gold to me.
And again, as mentioned above by others a couple times; just start playing with various styles, use the Multiriff function and start slicing/dicing, do a bluegrass tune and use grunge drums, or go the other way and try a fiddle in a rock tune .. just 'have fun'
I have to say though, getting 4 or 5 people together and just jamming is the most fun and inspiration for me. That feeling where everybody is looking at each other and 'dialed in' is pretty awesome. Look at how focused the band is on Barry in the picture below (he was giving the clues).
We're still 'in-process' here at the new location, the drums only have 2 mics on them in this picture! That won't last.
We've had some weird weather here recently, and this week electricity in the area was actually pretty scarce, but we'll do it again next week.
Someone also mentioned above about McCartney just making up lyrics in the beginning stages. That's common here. Build the groove first and fill in the lyrics after. Just how we roll.
The audio sample below shows just how that works here. This was our first hour into the song and nobody cares what the song is about yet; we're just getting a structure together.
/warning it's pretty much raw audio tracks from that night, nothing rerecorded yet, a work-in-progress very early on so you'll hear mistakes. We're still formulating the song after all. We're old but still having fun.
RB recorded audio from live session -
http://masteringmatters.com/stuff/170304C.WMA