What paint are you using? If you mean the nozzle is blocked it will need soaking and then use a long bristle paint brush to clean out inside gently.
If you use to much pressure you may damage the nozzle.
If your paint is running on the surface you are putting to much paint on the surface and not allowing it to dry before putting more paint over it.
You may be moving to slow and allowing the paint to build up, your PSI is to high or your paint is to thin.