When my printer isn't extruding much or its thin and stringy, I have a stiff wire (i stripped the plastic off the tie wrap from a loaf of bread) that I bend in a loop. I heat up the nozzle and when it reaches my typical printing temp I slide the wire into the nozzle and wiggle it around and up and down and then I immediately turn the extruder gear. Usually it dribbles out and then a large blob will come out and everything will be good after that.

Also to echo other folks, the distance to the print bed is pretty critical. Too much and the filament won't adhere to the bed, it dribbles and balls up all over and then sticks to the nozzle and makes a big mess. Too close and nothing comes out or its just tiny stringy blobs. Ive noticed that if I don't push a bit thru the hot nozzle after that happens (nozzle too close to the bed) then I get the nothing extruded issue.