Watch the Modulating online guitar lesson by Matthieu Brandt from Songwriting on Guitar
Moving to another tonal centre can create a contrasting mood in your composition. Depending on how many notes the original key and the key you modulated to share, this contrast will be great or more smooth. If the two keys you are using have many notes in common, you are modulating to a near key and the shock to the ear will be limited. You are modulating to a near key. If the two keys have few notes in common, the chords derived from those keys will also differ a lot. This is called modulating to a far key. These can really make the ear perk up.