Weller WE 1010 New Iron Tip Problem
Like others have suggested, the temperature you are running is likely too hot. You should always solder at the lowest possible temperature, and turn off your station during any breaks. Just doing this can significantly increase the lifespan of your soldering tips. The oxides form naturally on the surface due to air exposure, so keeping the tip tinned (and protecting the plating with a blanket of solder) will further slow this process.

Oxides can be removed by using a brass or copper cleaning sponge. Soldering tips are often copper that is coated in layers of iron, nickel, and chrome. Using steel wool or sand paper will easily scratch off this coating so be sure to avoid this.

I have had success bringing abused tips back to life by scrubbing with a brass sponge and then soaking the iron in a tin of flux for several seconds. You may need to cycle through this several times to fully clean the tip.  

Here is a resource with more information on extending soldering tip life (as well as various mechanical and abrasion failures that can occur)