Ideation requires us to diverge and converge. That is, to diverge is coming up with as many ideas as possible. To converge is narrowing down those ideas so that we can act upon them (eg. prototyping).
The following information has been contributed by Ben Weinlick and Aleeya Velji as Think Jar Collective in the Social Innovation Field Guide found here:
Learning how to come up with ideas and potential solutions to prototype is often a delicate process that needs some stewardship. Brainstorming often gets a bad rap because of a lack of understanding around the importance of safeguarding the required thinking modalities. People trying to ideate sometimes mix divergent thinking and convergent thinking at the wrong times and end up harming trust or throwing wet blankets on potentially good ideas.
Brainstorming can sometimes sound like a free-for-all activity but in the context of social innovation labs, it is a guided activity that helps foster creativity and innovation. It helps us think in different ways to come up with fresh, new ideas. It is important to be thoughtful and open to other people’s ideas and suggestions.
Source: Skills Society Action Lab

Examples and Resources

Wild Brainstorm Mashups

Set the stage for ideation/ brainstorming

Before beginning ideation, laying out some ground rules helps to keep ideas flowing and keeps our inner naysayer at bay during the process.
Source: Think Jar Collective & Skills Society Action Lab
Once your team has created 'How Might We..?' questions for your design challenge, you’re ready to start brainstorming! The intention of brainstorming is to leverage the creative power of the group by engaging with the full design team, listening carefully, and building on each other’s ideas.

Instructions: Brainstorming

1) Write out main question(s) Put up on the wall the main overarching challenge question (often a 'how might we... ?' question) that your lab is working on, and below that, the design criteria for the challenge question.
2) Gather the gear Share a stack of post-it notes and something to write with for each participant
3) Set the tone Review the Lab ground rules and divergent thinking guidelines
4) Brainstorm! Each participant writes down as many ideas as they can think of (1 idea per sticky note). Go for quantity of ideas, not quality (you can narrow them down later)
5) Set a timer and play some music
6) Try other divergent thinking exercises to open up new thinking Eg. See Nesta's Fast Idea Generator below 7) Share & Repeat Individuals share their ideas in groups, and repeat the individual brainstorming again. Repeat this process in consecutive rounds until you have many diverse ideas.
Nesta’s Fast Idea Generator which is helpful for brainstorming divergent ideas, is available here:
These are some creative problem-solving exercises that will open up new thinking and possibly spark something actionable (if you defer judgement at the outset and allow ideas to flow). For additional ideas, see Nesta's Fast Idea Generator.
New Connections
How might a user/ person that uses your service design a better solution? Or: how might a child approach the challenge? A senior citizen? Or a particular individual, such as Nelson Mandela?
Ideas from other fields
What interesting ideas have worked in other fields that you could apply to your challenge?
From other industries: E.g. How could we apply the streamlined customer experience of going to an Apple store to how we design social services?
By using biomimicry: E.g. an architect got an idea from termite hills for how to solve the challenge of making an air-conditioned building in the desert without electricity.
Reverse it
For a moment, try thinking of all the ways you could ensure the problem will never be solved.
What would you design if you were tasked with ensuring a service or system innovation could never happen? What would you have to do to ensure status quo reigned. What would keep the old ways going?