This will make you to an expert on using the Nikon D90, but this alone won't get great pictures. To get great photos you still need to get yourself to the right place and point the camera in the right direction at the right time, which is a lot harder than mastering the D90. Technically, lighting and the use or disuse of flash is far more important to artistic synthesis than your choice of camera.
Good Cleaning video How to Clean Your DSLR Sensor and Mirror----wow! I've been looking for this everywhere! I saw dirt on my mirror last month, and it's been bothering me ever since. (luckily it hasn't affected the pictures, though)