Do I need to clean an oven that's not been used in 10 years?
It should be fine to use.  It is probably dusty, perhaps greasy from other kitchen sources.  If it's self cleaning, go for it (and avoid using any harsh cleaners) It might get smoky at first, so you should have ventilation possible (window, fan, or whatever)
If not self cleaning, give it a good wiping-out with an ammonia based cleaner or use commercial oven cleaner(nasty stuff). If its possible that you have mice, you should probably make sure that they aren't nesting in the cabinet- get a technician if you aren't comfortable removing panels, etc. And buy an oven thermometer to check the oven thermostat. Self-cleaning or not, it will probably be smoky at first. Good luck.