I preface an answer with the fact that I think it's problematic to chop one's ideas down this dichotomy. Still, I will at least make a rough estimate, if not one that I'd want to be held up in any remotely important matter.
I used to lean much more toward thinking about what I was against. Eventually it became too frustrating to keep dismissing ideas without having anything to replace them. I no longer felt that I had any difficulty identifying problems, but it seemed pointless if I could not conceive of solutions. So, I tried to move much more toward identifying what I am for, and I've felt much more satisfied with my ideas ever since.
It's advice I'd give to anyone with similar positions as mine, people with certain ideas generally considered left wing but more specifically like social democracy, market socialism, restricting the profit motive, or fighting for financial equality. I think we spend too much time telling everyone what we think is wrong with corporatism, laissez-fair economics and the like. We should tell people about these things, but it's pointless if we cannot also provide an alternative and explain why we are for it.