This toolbox entry outlines different ways to brainstorm and ideate.

Tips & tricks

Set a time limit
As a facilitator, you need to be intentional about setting aside a period when your team will be in “brainstorm mode”. In this time frame, it’s the sole goal to come up with as many ideas as possible, and during this period judgements of those ideas are prohibited. Typically, a Brainstorm will take around 15-60 minutes. It can be shorter or longer, depending on the difficulty of the problem and the motivation and experience of the group.
Pro tip: “Invest energy into a short period of time, such as 15 or 30 minutes of high engagement. Get in front of a whiteboard or around a table, but take an active posture of standing or sitting upright. Get close together.” – dschool, Bootcamp Bootleg

Start with a problem statement, Point of View, How Might We questions, a plan or a goal – and stay focused on the topic
Brainstorming sessions should always address a specific question or problem statement (also called a Point of View) as sessions addressing multiple questions are inefficient. Begin with a good problem statement or question. 
Pro tip: “Write down clearly what you are brainstorming. Using a ‘How Might We’ (HMW) question is a great way to frame a brainstorm (e.g. HMW give each shopper a personal checkout experience?).”
– dschool, Bootcamp Bootleg

Defer judgement or criticism, including non-verbal and encourage weird, wacky, and wild ideas
A Brainstorming session is not the time and the place to evaluate ideas, and you should avoid executional details. It’s crucial that participants are feeling confident by being in a safe environment so they have no fear of being judged by others when they put forward wild ideas.

Aim for quantity
Aim for as many new ideas as possible. The assumption is that the greater the number of ideas you generate, the bigger your chance is of producing a radical and effective solution. 

Build on each others' ideas
Brainstorming works well when participants use each other's ideas to trigger their own thinking. Our minds are highly associative. One thought easily triggers another. When we use the thoughts of others, then these will stop us getting trapped by our own thinking structures.

Be visual
Nothing gets an idea across faster than drawing it. 

Don’t get obsessed with your own ideas. 
You’re here to ideate together.