Begin in the middle
Begin a scene in the middle, so you don't have to start it. Never start things, only respond to stuff that's already there.
I love this one. Especially the second part: only respond.
All too often, at the start of a scene, improvisers are in their heads thinking of WWW or CROW or other theories. Of course you can endow your partners on stage, but don't label them. They need an emotional state, not a business card. Ideally, your partner goes "Aah, yes, that makes sense!" after every endowment at the beginning of a scene and not "Oh... ok, I can do that.".
Don't be afraid that there is nothing there, since there always is. Loads of stuff. Once you realise that, you probably won't even need or enjoy an audience suggestion anymore to get started.
Remember to always begin in the present however. A sentence like "You did well" lives in the past and "There is so much work to do" lives in the future. Try "I'm enjoying this so much". That lives in the present.