I am very suspicious about being too quick to label ideas as either good or bad. That way we risk spending a lot of time and energy on ideas which turn out to be pants. And we can be very dismissive of ideas which someone else turns into a gold mine.
But we can use the labels of "good" and "bad" to sift and develop our ideas. Something like this:
Idea generation
In this stage there are no bad ideas. The important thing is to generate as many possible ideas as we can. Be super-optimistic and turn off that nagging voice which is talking about cost and risk. Ideas are usually created by tacking two concepts together (but that's a whole different area).
Idea development and championing
Take each idea in turn and tell yourself that this is the most fabulous idea that anyone has ever had. Your job is to make it work, no matter what it takes. You can turn the volume up a little on the nagging cost/risk voice, but now you are in problem-solving mode. Find a solution to every negative that the black hat comes up with. Ask yourself the open question of power: "how could I make this work?" Don't ask the closed question of "will this work?" because that invites a false yes or no. We might drop a few stone-cold turkeys at this point, but we are really looking to give each idea the best chance it can have.
Judgement
Now we need to balance optimism against caution. Sift the ideas into bad, promising, dubious or whatever categories work for you. Prioritise. Rank them in order. Sometimes we emerge with just one gleaming idea. Sometimes we end up with several, or none. This is the first time we are allowed to talk openly about good vs bad ideas. This is when we need to make choices to filter lots of ideas down to one or two.
Stress-test to destruction
Now we put our black hat firmly on our heads for any remaining options. This is the time to be as cynical as we can be. We need to test the idea to breaking point. A weak idea will wilt at this stage, which is why we have saved this stage til nearly last. If we did this straight away, all of the ideas would probably fail. But by now our last few ideas left standing have a lot of positivity from the idea development stage. There might need to be some iteration between this stage and the preceding two until we can make a decision.
Execute
Now we go away and do it, secure in the knowledge that any idea that has survived this process ought to have something going for it. Solve any problems that come up. Keep testing, keep refining. Have faith in yourself.
The whole thing may sound long-winded but you get faster at it with practice. Honest.