The Lydian mode starts on the fourth scale degree and like the corresponding chord is major in nature. It has been described as having a modern sound, giving drive or momentum.
In the Key of C : C D E F G A B C the fourth scale degree is F so we have an F Lydian in this Key.
F Lydian: F G A B C D E F The intervals are therefore T T T S T T S
If we compare to F Major : F G A Bb C D E F we can see that the Lydian mode has a #4 compared to the corresponding major scale. It is this #4 that gives the Lydian mode that feeling of musical momentum.
An example pattern starting on the A string is shown below. I’ve started on the A string to keep the fingering pattern fairly uniform. As with all the modes, you definitely want to experiment a lot with playing this pattern in as many different positions as possible (audio here):
If you need a diagram showing the notes on the fretboard, one is available in the Ionian mode (Major scale) post.
How you play these modes is really up to you. You could use a Lydian mode all of the time as it will fit with any chord in the key. For variety you can mix them around a bit, often minor modes will be used over minor chords and major modes will be used over major chords. The best thing is to experiment with voicings and phrasings to find the sort of sounds that you like.
As an example to get you started, I’ve created a simple F F C C F F C C (IV I) 8 bar chord progression which has the Lydian mode played over the top of it as shown below. It’s a simple pattern just to give you an idea of the sound. (Audio here)
Good luck, and the most important thing – have fun!