Watch the Slidin' Sixths online guitar lesson by Jeff McErlain from 50 Blues Rock Guitar Licks You MUST Know
The interval of the 6th is one of the most useful and common in blues. The cool thing about it and why it sounds so good is that it is an inverted 3rd. What? Let's look at it, a major 3rd above C is E, a major 6th above E is C. Pretty cool and extremely useful. I can't stress enough memorizing your 6ths on the fingerboard, they will provide you with plenty of mileage and increase your understanding of the guitar. So while you are at it, practice all your intervals!