This question has been asked before. I believe motordavid had given a good response to a previous thread on this issue.
My 2 cents
Fill the tank and add algicide
Drying agent like calcium carbonate inside the cabin
Do a full underbody wash...as clean as possible
Air blast all the drain holes
Stuff the exhauts and stick a note on steering to unstuff(rats, insects etc like to live there)
Probably jack the car.