Also I recommend stocking up on extruder nozzle de-cloggers. They're these little delicate needles that look like microscopic drill bits; you use them from the bottom up while the extruder is heated (careful not to get hot plastic on your fingers or touch the extruder nozzle!). Sometimes that helps to remove gunk filament that's gotten clogged at the nozzle end. If you're still having problems after trying to unload and reload the filament, then definitely take the extruder apart. Make sure you have NO space between the nozzle throat tube and the filament extruder drive; if there's any open space it can cause havok when the filament is feeding through. Your fan is running 100% speed when you're extruding, yes? It should automatically turn on with most slicing software settings...