Watch the Triads online guitar lesson by Robert Renman from Blues Booster
Triads are everwhere. They are also chord tones, so knowing the triads for the chords you are playing over is extremely useful. The triads are also part of my Hybrid scale. Look at R, Triangle3 and M5 in the diagrams. Those are 1-3-5, the triads. Triads are so useful, not just in blues, but in any style of music. You can view them as building blocks, and as a foundation for licks and ideas. Practice and learn to instantly find 1-3-5 for any chord you are playing over, and you'll never sound bad!