Normalization is less important for sound effects, foley and music, but it is imperative for dialogue clips. Normalizing your dialogue will ensure that all these clips are around the same basic volume. Most DAWs and NLEs have a built-in normalizing plugin, and it’s just a matter of dropping that plugin onto your audio clips or on to the entire audio track, and setting the plugin to normalize your audio. At this stage, normalizing your dialogue to around -3dB should be sufficient.

The problem with normalizing is that most of the plugins available normalize based on the peaks in the audio, and not the general loudness. Any clips that are mostly quiet save for a few loud peaks might not be raised in level very much, while those that are consistent (without peaks) at a medium volume level may be turned up more! 

This is why it’s important to not just rely on the tools you’re using, but also your ears. After normalizing your audio, review the dialogue and tweak the levels of each individual clip to make sure they have the same general volume.