Let's take a look at the construction of the modes:
Ionian - 1, 2, 3, 4, 5, 6, 7
Dorian - 1, 2, b3, 4, 5, 6, b7
Phrygian - 1, b2, b3, 4, 5, b6, b7
Lydian - 1, 2, 3, sharp 4th, 5, 6, 7
Mixolydian - 1, 2, 3, 4, 5, 6, s6
Aeolian - 1, 2, b3, 4, 5, b6, b7
Locrian - 1, b2, b3, 4, b5, b6, b7
In the key of C major it would be like this:
The sound does not seem any different apart from starting from a different note of the major scale. But here is the trick that is so simple yet very effective.
Keep the key the same but change the mode.
For example if you are writing or improvising in the key of C major, instead of playing C Ionian play C Lydian.
Lydian is generally the brightest of those modes due to the structure of those two modes. The Lydian is like Ionian but with a sharped perfect 4th. This would make the tritone meaning that you can make the Lydian sound really dark in depending on the notes you use and the chords you play over.
G Lydian. Instead play G Locrian.
Locrian generally has the darkest feel of the modes. Look at how many dissonant intervals that make the structure of the mode. We have b2, b5, b7. Locrian is Aeolian with flatted 2nd and tritone. So you can see how this mode is so dark. But any mode can be made to sound bright dark or something in between depending on which notes you use over the chords you choose to play over.
If you want to make a general change in sound straight away before you think about chords, changing the mode and keeping the key the same is a great effective way to change the feel of your guitar playing. This can be applied to harmonic minor modes, melodic minor modes and you can apply this concept for any other scale as well.