Noise Reduction for Dialog

There's a couple things you can do. One is to use a broadband noise reducer. This would be like the Waves Dynamic Noise Suppression. It helps eliminate fairly "steady state" noises like fans and traffic and rain and such. 

Another noise reducer is a Spectral noise reduction. I have one of these built into Samplitude. This is good for bumps, hits, and crackles (even footsteps). But it's a fairly tedious thing to use.

I actually cheat and I assign all of my dialog to a buss with (fairly heavy) noise reduction slapped across it. Then when things get really noisy I go in and add even more noise reduction to the passages which are a problem. Then I turn up the Foley or other background noise beds.