One of Freddie King’s trademarks was to include sixth intervals in his melodies.
In this case we race across the neck in different positions to include most playable sixth intervals on the IV chord.

Remember to move with the chords when you’re playing these types of riffs.

What he was further known for was his quick rasping of small arpeggios on the top string, here seen on the V and VI chord.
Make sure to bend the end notes of these riffs 1/4 up to get a real bluesy sound.

Last but not least Freddie liked to move quickly up and down all blues positions; going from the first blues position immediately to the fourth and back.
This is seen in the last riff on the V chord.